Electrode for electrochemical measurement, electrolysis cell for electrochemical measurement, analyzer for electrochemical measurement, and methods for producing same

ABSTRACT

Provided are an electrode, an electrolysis cell, and an electrochemical analyzer that improve the long-term stability of analysis data. A working electrode, a counter electrode, and reference electrode are disposed in an electrolysis cell. The working electrode is obtained by forming a lead wire in a composite material having platinum or a platinum alloy as a base material, in which a metal oxide is dispersed, or in a laminated material obtained by laminating a valve metal and platinum such that the cross sectional crystal texture in the thickness direction of the platinum is formed in layers and the thickness of each layer of the platinum is 5 micrometers or less. The metal oxide is selected from among zirconium oxide, tantalum oxide, and niobium oxide, and the metal oxide content of the platinum or the platinum alloy is 0.005 to 1 wt % in terms of the zirconium, tantalum, or niobium metal.

TECHNICAL FIELD

The present invention relates to electrodes for electrochemicalmeasurement, electrolysis cells for electrochemical measurement, anelectrochemical analysis apparatus, and manufacturing methods thereof;more particularly, it relates to an electrode for electrochemicalmeasurement, an electrolysis cell for electrochemical measurement, andan analyzer for electrochemical analysis with which minute amounts ofchemical components contained in liquid samples such as blood and urineare analyzed electrochemically.

BACKGROUND ART

Electrochemical measurement is capable of performing high-sensitivitymeasurement with use of relatively simple apparatus configurations andis frequently used in the field of analytical chemistry. Availableelectrochemical measurement schemes include potentiometry, amperometry,voltammetry, and impedance measurement, and further include otherdetection methods such as methods for detecting photons by combinatorialuse of these with an optical element or the like, for example.

Generally, an electrode used for electrochemical measurement isfrequently made of a platinum group metal—especially, platinum—in thelight of its excellent chemical stability characteristics. In recentyears, also in the analysis of chemical components contained in liquidsamples such as blood and urine, platinum is used as the electrode to bebuilt in a flow cell.

For example, Patent Literature 1 discloses that in the case ofcontinuous measurement of a chemical component in blood or urinerepetitive measurement is enabled through a process of applying aplurality of electrical potentials between a working electrode and acounter electrode on a per-analysis basis, in addition to cleaning andmain measurement.

An example using a mixture material of platinum and metal oxide as theelectrode is found in Patent Literature 2, which discloses therein anelectrode comprising a surface layer formed on the surface of a metallicbase substance by solid solution of tin oxide and antimony oxide and amixture layer of a platinum-group metal or its oxide and an oxide of IV-or V-group metal as an intermediate layer between the metal basesubstance and the surface layer. Additionally, Patent Literature 3discloses an electrode for electrolysis having an outer layer above asurface of a titanium or a titanium alloy body with an intermediatelayer being laid therebetween, wherein the outer layer is made of amixed metal oxide comprising iridium oxide, platinum, and at least onekind of metal oxide selected from the group consisting of niobium oxide,tantalum oxide, and zirconium oxide.

Patent Literature 4 discloses therein an oxygen sensor's electrodecomprising either an oxide semiconductor or a solid electrolyte, thesurface of which is coated with an electrode material containing anoxide of aforementioned the aforementioned constituent metal andplatinum.

Concerning the electrode material containing a platinum-group metal,Patent Literature 5 describes therein use of a platinum-group metal forthe counter electrode and the working electrode. Additionally, PatentLiterature 6 discloses an electrode for electrochemical reaction whichis composed with a valve metal such as titanium, tantalum, or zirconiumand platinum by thermal pressing, and also discloses a manufacturingmethod of the electrode.

Furthermore, Patent Literature 7 discloses an electrode with sequentialformation of a platinum alloy coat layer and a coat layer made ofiridium oxide and/or platinum oxide on a titanium, niobium, or tantalumbase material, as an electrode for electrolyzing a salt solution toproduce strongly acidic water having bactericidal action and aninsoluble electrode used for certain applications such as electrolyticcleaning treatment of waste water containing organic substances.

CITATION LIST Patent Literature

-   Patent Literature 1: JP-A-06-222037-   Patent Literature 2: JP-A-2010-095764-   Patent Literature 3: JP-A-02-200790-   Patent Literature 4: JP-A-05-180796-   Patent Literature 5: JP-A-10-288592-   Patent Literature 6: JP-A-02-066188-   Patent Literature 7: JP-A-2001-262388

SUMMARY OF INVENTION Technical Problem

In cases where a platinum-group metal, especially platinum, is used asan electrode, it shows very excellent characteristics in analyses to beexperimentally performed for a few dozen times to several hundred times.

However, in the analysis system shown in Patent Literature 1, forexample, in the analysis of chemical components contained in a liquidsample such as blood or urine, the electrode surface is graduallycorroded in a case where a sample that contains large amounts of proteinand halogen elements in its components is subjected to iterativemeasurement for a long time period or, alternatively, in case a samplecontaining a strong alkaline component such as potassium hydroxide as acleaning agent for cleaning an electrode surface is brought into contactwith the electrode surface and then a voltage is repeatedly appliedthereto for a prolonged period. As a result, the electrode's surfacecondition varies, posing a problem that it exerts a bad influence onmeasurement results.

In Patent Literature 2, a mixture material of platinum and metal oxideis used as the intermediate layer in order to improve adhesiveness andelectrical conductivity between a metal base substance and a solidsolution of tin oxide and antimony oxide actually causingelectrochemical reaction. In Literature 2, the mixture material ofplatinum and metal oxide is not used as the surface for causingelectrochemical reaction. Although the solid solution of tin oxide andantimony oxide becomes the surface actually causing electrochemicalreaction, with samples containing strong alkaline component as intendedby the present inventors dissolution from the electrode surface islarge, thereby causing the surface state to vary significantly andresulting in a failure in improving the stability of analytical data.

Although in Patent Literature 3 the outer layer's mixed metal oxide isan electrode material formed by sintering and it is known thataforementioned material exerts effect as an anode for seawaterelectrolysis, metal surface treatment, metal foil fabrication/recovery,and the like, wastage of the electrode is severe with an increase invariation of electrode surface state, resulting in lessened effect onimprovement of the stability of analysis data in the inventors' intendedcase of iteratively performing measurement of a sample containing largeamounts of protein and halogen element in its components for an extendedperiod of time or, alternatively, in the case of iteratively applying avoltage over time while contacting a sample with the electrode surface,where sample contains a strong alkaline component such as potassiumhydroxide, as the cleaning agent for cleaning the electrode surface. Inaddition, due to the presence of cracks in the electrode surface of theaforementioned material, it was seen in some cases that residue of theliquid sample adversely affects a measurement result of the next sample.

In Patent Literature 4, in the case of letting stabilized zirconia be asolid electrolyte for a detection electrode of an oxygen sensor forexample, its surface is coated with a mixture of platinum and zirconiumoxide, thereby improving adhesion with the underlying solid electrolyteand also achieving improvement of reaction efficiency owing to theformation of a three-phase interface. Although details are not disclosedtherein, it is considered that the platinum/zirconium mixture is low infilm density in view of the fact that an advantage of reactionefficiency improvement was obtained. More specifically, it isconceivable that the aforementioned mixture as the electrode foriterative measurement of chemical components contained in a liquidsample as intended by the inventors can result in a decrease inreliability of measurement result due to residue of the liquid sample ina film.

As is commonly known, platinum is a high-priced metal and, as shown inPatent Literatures 5 and 6, it is well known to employ compositeelectrodes made of compounds of a platinum-group metal, platinum, atitanium metal, and the like.

However, in the above-stated composite electrodes, there are no examplesarranged to control the crystalline texture and orientation property ofa platinum layer.

The inventors of the present application have conducted diligent studiesto reveal that analysis data are affected by the surface state of theelectrode—particularly, the crystalline texture and crystal orientationproperty—in the analysis that uses the same electrode to measure aplurality of times a very small concentration of chemical componentcontained in a liquid sample such as blood or urine.

It is an objective of the present invention to realize an electrodecapable of performing proper analytical measurement while letting dataremain stable over a lengthy period, an electrolysis cell using thiselectrode, and an electrochemical analysis apparatus using the same.

Furthermore, it is another object of the present invention to realize anelectrode for the electrochemical measurement use which reduces theamount of platinum and has enough mechanical strength but is less invariability of electrode surface state, an electrode capable ofperforming adequate analytical measurement with long-term data stabilityby using the aforementioned electrode, and an electrolysis cell and anelectrochemical analysis apparatus using such the electrode.

Solution to Problem

To attain the foregoing objects, the present invention is arranged asfollows.

An electrode of the present invention is an electrode forelectrochemical measurement used in an electrochemical analysisapparatus which measures electrochemical response of a chemicalcomponent contained in a liquid sample and is an electrode which is madeby forming a lead wire to a composite material in which a metal oxide iscontained as being dispersed in a base material that is made of platinumor a platinum alloy. As the metal oxide zirconium oxide, tantalum oxide,niobium oxide, or the like is preferable and the content ratio in theplatinum or the platinum alloy is set at 0.005 to 1% in themetal-equivalent value. It is noted that the percentage of the contentratio of a chemical component in this description is designated inweight percent (wt %).

The electrode of the present invention is an electrode in which theorientation ratio of one of a plurality of crystal directions obtainedis 80% or greater when letting the orientation ratio (%) of a crystaldirection obtained by X-ray diffraction measurement of a surface of theelectrode be I(hkl)/ΣI(hkl)×100 (where I(hkl) is a diffraction intensityintegration value of each plane, and ΣI(hkl) is the total sum ofdiffraction intensity integration values of (hkl)).

The electrode of the present invention is an electrode in which amaterial of an electrode is embedded in an insulative resin except for apart of the surface of the electrode.

An electrolysis cell of the present invention is an electrolysis cellfor measuring electrochemical response of a chemical component containedin a liquid sample and is an electrolysis cell which has theabove-stated electrodes of this invention as a counter electrode, areference electrode, and a working electrode disposed inside the cell.It may alternatively be a flow cell to which an injection port forinjecting into the cell and an exhaust port for discharging to exteriorof the cell a liquid sample are disposed.

An electrochemical analysis apparatus of the present invention is anelectrochemical analyzer which includes the above-stated electrolysiscell of this invention; a solution injection means which injects intothe electrolysis cell a solution to be measured, a buffer solution, anda cleaning solution; a potential application means which appliespotentials to the working electrode, the counter electrode, and thereference electrode; and a measuring means which is connected to theworking electrode, the counter electrode, and the reference electrode,and measures electrochemical characteristics of the solution to bemeasured.

A method for producing an electrode for electrochemical measurement ofthe present invention is a method following the steps (a) to (d) below.

The steps comprise (a) electroding by providing a lead wire to acomposite material in which a metal oxide is contained as beingdispersed in a base material, which is made of platinum or a platinumalloy (b) embedding the electrode in an insulative resin except for onepart of a surface of the electrode, (c) performing mechanical polishingon a surface of the electrode embedded in the resin, and (d) performingelectrolytic polishing on the surface of the electrode to remove asurface alteration layer. It is preferable that the electrolyticpolishing is a step of iteratively applying for a plurality of times apotential between potentials of from a hydrogen producing region to anoxygen producing region in an electrolytic solution. It is preferablethat a waveform of the applied potential is a rectangular wave. It isfurther preferable that, after the electrolytic polishing processing,cyclic voltammetry is carried out so that a state of a surface of anelectrode is diagnosed from the area ratio of at least two of aplurality of hydrogen absorption/desorption peaks seen in themeasurement result and electrolytic polishing is repeated until aprescribed peak ratio is reached.

A method for producing the electrolysis cell of the present invention isa method following the steps (a) to (e) below.

The steps comprise (a) electroding by providing a lead wire to acomposite material in which a metal oxide is contained as beingdispersed in the base material, which is made of platinum or a platinumalloy, (b) embedding the electrode by an adhesive agent into aninsulative substrate having a solution injection port and an exhaustport formed in advance, (c) performing mechanical polishing on a surfaceof the electrode embedded in the insulative substrate, (d) performingelectrolytic polishing on the surface of the electrode to remove asurface alteration layer, and (e) integrating by lamination theinsulative substrate with the electrode on which polishing was performedbeing embedded therein, a sealing member having an opening, and anotherinsulative substrate, and adding thereto a counter electrode and areference electrode.

An apparatus for producing an electrode for electrochemical measurementof the present invention is a manufacturing apparatus which comprises(a) an electroding unit which provides a lead wire to a compositematerial in which a metal oxide is contained in as being dispersed inthe base material, which is made of platinum or a platinum allow, (b) aresin embedding unit which embeds the electrode in an insulative resinexcept for one part of a surface of the electrode, (c) a mechanicalpolishing unit which performs mechanical polishing on a surface of theelectrode embedded in the resin, and (d) an electrolytic polishing unitwhich performs electrolytic polishing on the surface of the electrodesurface to remove a surface alteration layer.

An apparatus for producing an electrolysis cell of the present inventionis a manufacturing apparatus which comprises (a) an electroding unitwhich provides a lead wire to a composite material in which a metaloxide is contained as being dispersed in the base material, which ismade of platinum or a platinum allow, (b) a resin embedding unit whichembeds the electrode by an adhesive agent into an insulative substratehaving a solution injection port and an exhaust port formed in advance,(c) a mechanical polishing unit which performs mechanical polishing on asurface of an electrode embedded in the insulative substrate, (d) anelectrolytic polishing unit which performs electrolytic polishing on thesurface of the electrode to remove a surface alteration layer, and (e) acell assembling unit which integrates by lamination the insulativesubstrate with the electrode on which polishing was performed beingembedded therein, a sealing member having an opening, and anotherinsulative substrate, and adds thereto a counter electrode and areference electrode.

The electrode for electrochemical measurement of the present inventionis arranged so that a valve metal of any of Ti, Ta, Nb, Zr, Hf, V, Mo,and W and platinum are laminated with each other and a cross-sectionalcrystal texture of the platinum part in the plate thickness direction isformed in a layer-like form with respect to the surface of theelectrode.

Also, an electrochemical analysis apparatus of the present inventioncomprises an electrolysis cell having a working electrode, a counterelectrode, and a reference electrode disposed therein; a solutioninjection mechanism which injects a solution under measurement and abuffer solution in the electrolysis cell; a potential application meanswhich applies potentials to the working electrode, the counterelectrode, and the reference electrode; and a measuring means which isconnected to the working electrode, the counter electrode, and thereference electrode and measures electrochemical characteristics of thesolution under measurement, in which the working electrode has a valvemetal of any of Ti, Ta, Nb, Zr, Hf, V, Mo, and W and platinum beinglaminated with each other, and a cross-sectional crystal texture of theplatinum part in the plate thickness direction being formed in alayer-like form with respect to the surface of the electrode.

Furthermore, a method for producing an electrode for electrochemicalmeasurement to be used in an electrochemical analysis apparatus of thepresent invention comprises the steps of forming a multilayer electrodeas laminating a valve metal of any of Ti, Ta, Nb, Zr, Hf, V, Mo, and Wand platinum into a plate-like form by cold rolling so that across-sectional crystal texture in plate thickness direction of theplatinum in a layer-like form with respect to a surface of an electrodewith a thickness of each layer of the platinum being equal to or lessthan 5 micrometers, performing mechanical polishing on the formedmultilayer electrode, and electrochemically removing a surfacealteration layer of the multilayer electrode.

Further, an apparatus for producing an electrode for electrochemicalmeasurement to be used in an electrochemical analysis apparatus of thepresent invention comprises a platinum plate machining unit whichproduces a platinum plate with a prescribed plate thickness as pressingplatinum in a nitrogen atmosphere and heating it to perform hot rolling,a platinum plate cold-rolling unit which cold rolls the platinum plate,a surface oxide film removing unit which places the platinum plateprocessed at the platinum plate cold-rolling unit and a titanium platein a vacuum and dry etches a surface of the titanium plate so that asurface oxide layer is removed, a multilayer electrode forming unitwhich forms a multilayer electrode of platinum and titanium aslaminating the platinum plate and the titanium plate and performing coldrolling in a vacuum atmosphere in such a manner that a film thickness ofthe platinum plate becomes a prescribed thickness so that across-sectional crystal texture in a plate thickness direction of theplatinum in a layer-like form with respect to a surface of the electrodewith a thickness of each layer of the platinum is equal to or less than5 micrometers, a cutting unit which cuts the formed multilayer electrodeinto a prescribed size, an electroding unit which connects electricallya platinum surface of the cut multilayer electrode and a conductive wiretogether, a resin embedding unit which embeds in an insulative resinusing an adhesive agent in such a manner that only a platinum surface ofthe multilayer electrode connected with the conductive wire is exposedwith a prescribed area, a mechanical polishing unit which performsmechanical polishing on the platinum surface of the embedded multilayerelectrode, and an electrolytic polishing unit which repeats scanning ofelectrical potential to the mechanically polished multilayer electrodein an electrolytic solution at a prescribed potential and a prescribedpotential scanning rate.

Advantageous Effects of Invention

According to the present invention, by using an electrode which is madeby forming a lead wire to a composite material in which a metal oxide iscontained as being dispersed in a base material that is made of platinumor a platinum alloy, preferably, the electrode in which the metal oxideis zirconium oxide, tantalum oxide, or niobium oxide and its contentratio in the platinum or the platinum alloy is set at 0.005 to 1% in themetal-equivalent value, particularly, the electrode in which theorientation ratio of one of a plurality of crystal directions obtainedby X-ray diffraction measurement of a surface of the electrode surfaceis 80% or greater, and the electrolysis cell and the electrochemicalanalysis apparatus using such the electrode, it becomes possible tosecure the state of the surface of the electrode which is stable in along term and obtain measurement results with high reliability in theelectrochemical analysis for measuring electrochemical response of achemical component contained in a liquid sample, in particular, in theanalysis that performs iterative measurement of a chemical componentcontained in a liquid sample such as blood or urine.

Furthermore, according to the present invention, it is possible torealize an electrode for electrochemical measurement which reduces theamount of platinum and has enough mechanical strength but is less invariation of electrode surface state, an electrochemical analysisapparatus using this electrode and capable of performing properanalytical measurement with long-term data stability, a manufacturingmethod of the electrode for electrochemical measurement, and amanufacturing apparatus of the electrode for electrochemicalmeasurement.

Other objects, features, and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overall configuration diagram of an electrochemicalanalysis apparatus in accordance with one embodiment of the presentinvention;

FIG. 2 is a schematic configuration diagram of an electrodemanufacturing apparatus for electrode for an electrochemical measurementapparatus in accordance with one embodiment of the present invention;

FIG. 3 is a configuration diagram of an electrode used forelectrochemical measurement in accordance with one embodiment of thepresent invention;

FIG. 4 is a diagram showing a cross-sectional structure along A-A′ planeof FIG. 3;

FIG. 5 shows X-ray diffraction analysis results of electrodes of oneembodiment of the present invention and one comparative example;

FIG. 6 is a diagram for explanation of effects of an electrode based onone embodiment of the present invention;

FIG. 7 is a configuration diagram of an electrode for electrode forelectrochemical measurement in accordance with one embodiment of thepresent invention;

FIG. 8 is a configuration diagram in the case of viewing from a sideface of FIG. 7;

FIG. 9 is a cyclic voltammogram of electrodes of one embodiment of thepresent invention and one comparative example;

FIG. 10 is an overall configuration diagram of an electrochemicalanalysis apparatus in accordance with one embodiment of the presentinvention;

FIG. 11A is an exploded configuration diagram of a flow cell used for anelectrochemical analysis apparatus in accordance with one embodiment ofthe present invention;

FIG. 11B is a cross-sectional assembly diagram of the flow cell used foran electrochemical analysis apparatus in accordance with one embodimentof the present invention;

FIG. 12A is an exploded configuration diagram of another example of theflow cell used for an electrochemical analysis apparatus of anembodiment of the present invention;

FIG. 12B is a cross-sectional assembly diagram of another example of theflow cell used for an electrochemical analysis apparatus of anembodiment of the present invention;

FIG. 13A is an exploded configuration diagram of a further example ofthe flow cell used for an electrochemical analysis apparatus of anembodiment of the present invention;

FIG. 13B is a cross-sectional assembly diagram of a further example ofthe flow cell used for an electrochemical analysis apparatus of anembodiment of the present invention;

FIG. 14A is an exploded configuration diagram of another further exampleof the flow cell used for an electrochemical analysis apparatus of anembodiment of the present invention;

FIG. 14B is a cross-sectional assembly diagram of another furtherexample of the flow cell used for an electrochemical analysis apparatusof an embodiment of the present invention;

FIG. 14C is a cross-sectional view of an insulative substrate in anotherfurther example of the flow cell used for an electrochemical analysisapparatus of an embodiment of the present invention;

FIG. 15 is a cross-sectional assembly diagram of still another furtherexample of the flow cell used for an electrochemical analysis apparatusof an embodiment of the present invention;

FIG. 16 is a schematic configuration diagram of an electrolysis cellmanufacturing apparatus in accordance with one embodiment of the presentinvention;

FIG. 17 is a table showing content rates of added metal oxide,preferential orientations of platinum or platinum alloy as a basematerial, analytes, and variation ranges of Embodiments 1 to 14 of thepresent invention and Comparative Examples 1 to 9;

FIG. 18 is a schematic configuration diagram of a manufacturingapparatus of an electrode for electrochemical measurement in accordancewith one embodiment of the present invention;

FIG. 19 is a diagram showing X-ray diffraction analysis results ofelectrodes of one embodiment of the present invention and onecomparative example;

FIG. 20A is a diagram showing an analysis result of crystalline textureof a cross-section in the plate thickness direction of an electrode inaccordance with one embodiment of the present invention;

FIG. 20B is a magnified diagram showing a near-surface analysis resultof crystal texture of a cross-section in the plate thickness directionof an electrode in accordance with one embodiment of the presentinvention;

FIG. 21 is a diagram for explanation of effects of a platinum electrodebased on one embodiment of the present invention;

FIG. 22 is a cyclic voltammogram of electrodes of one embodiment of thepresent invention and that of a comparative example;

FIG. 23 is a diagram showing an analysis result of crystalline textureof a cross-section in the plate thickness direction of an electrode ofone comparative example different from the present invention; and

FIG. 24 is a table showing preferential orientations of platinum part,analytes, and variation ranges of Embodiments 15 to 25 of the presentinvention and Comparative Examples 10 to 18.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be explained with reference tothe accompanying drawings below.

Prior to explanation of embodiments of the present invention, anexplanation will be given on principal concepts of the presentinvention.

The inventors performed analysis, in various ways, about the cause forvariation of measurement results in cases where measurement isrepeatedly carried out over an extended time period in the analysis ofchemical components contained in a liquid sample such as blood or urine.As a result, it was revealed that it arises mainly from changes inelectrode surface state due to iteration of analysis.

Namely, when repeating over time the process of applying electricalpotential in a liquid sample containing therein protein or the like andthe process of applying electrical potential in a liquid containing astrong alkali component such as potassium hydroxide serving as acleaning agent for cleaning an electrode surface, the electrode surfaceis gradually etched away, causing the state of a surface after iterativeanalyses to vary from that at the initial stage of analysis. Thisadversely affects a measurement result as result.

Upon inspection of the platinum surface's etching behavior, in the caseof a platinum electrode with its crystalline texture coarsened due tothermal processing for example, a case was seen where with repeatedexecution of analysis, an easily etchable crystal face preferentiallyundergoes elution, causing local generation of a relatively largeconcave portion within the electrode surface. This arises from a changein etching rate depending on the surface's crystal direction. It wasalso revealed that in the case of a certain chemical component containedin the liquid sample, the reactivity differs depending on the crystaldirection of electrode surface. Namely, it was ascertained that repeatedanalysis execution causes the ratio of each crystal direction exposed tothe outermost surface to vary, resulting in the response amount ofelectrochemical reaction becoming different, thereby affecting analysisdata. This phenomenon is such that in the case of placing the electrodein a flow cell, it is no longer possible to establish stable liquidflow, resulting in a failure to sufficiently perform the substitution ofan analyte liquid and cleaning liquid, thereby disabling execution ofadequate analysis.

Meanwhile, in cases where an electrode is used which is made finer incrystalline texture and has its crystal orientation propertypreferentially aligned to one direction, it was found out that evenunder the condition where the electrode surface is etched due toanalysis iteration, the elution caused by etching progresses relativelyuniformly in an electrode plane without forming local concave portionsin the electrode plane, although it experiences generation of a numberof fine holes formed by the etching, i.e., etch pits. Especially, in asystem for selectively capturing a minute concentration of chemicalcomponent contained in a liquid sample such as blood or urine on theelectrode using magnetic particles to analyze particles, it was foundthat the frictional force between etch pits created in the surface andmagnetic particles increases, resulting in improvement of the stabilityof magnetic particles on the electrode, which in turn leads tostabilization of analysis data.

For the reason stated above, the conception was reached in which forimprovement of the analysis data stability, it is effective thatcrystalline structure of an electrode material which actually causeselectrochemical reaction is fine and that variation of the exposedcrystal face under the condition that its surface is gradually etchedaway is suppressed.

One of electrode materials of the present invention is an oxidedispersion type composite material with a metal oxide being finelydispersed in a base material of either platinum or platinum alloy, aswill be explained in greater detail below.

Concerning the platinum or the platinum alloy as the base material ofthe electrode of the present invention, platinum-rhodium, platinum-gold,platinum-iridium, or the like is selectable appropriately in accordancewith the chemical component contained in a liquid sample. In the metaloxide dispersion type composite material as disclosed herein, the basematerial is either platinum or a platinum alloy in the bulk state And,when defining a void ratio to be a volume-equivalent percentage value ofthe ratio of voids existing in the base material to the base material,it is a material with its void ratio being less than or equal to1%—preferably, 0.2% or less. Preferably, the hole diameters of the voidsare 5 μm or less. When the void ratio goes above 1% and/or the holediameters of voids exceed 5 μm, the voids existing in the base materialare exposed to the top surface in the process of analysis iteration,thereby affecting analysis data in some cases.

The metal oxide in the metal oxide-dispersed composite material of thepresent invention stably exists in either the platinum or the platinumalloy that is the base material in a fabrication process of thecomposite material and serves, as one of its roles, to keep the basematerial's crystal texture fine. Desirably, the metal oxide existing inthe electrode surface is the one that is small in contribution toelectrochemical reaction within a wide pH range since it contacts withvarious kinds of electrolytic solutions such as a liquid sample. As canbe seen from these reasons and a potential-pH diagram (Pourbaixdiagram), oxides of zirconium, tantalum, niobium, or the like areusable.

Preferably, the content ratio of such metal oxide in the base materialfalls within a range of from 0.005 to 1%. In the case of being equal toor less than 0.005%, the amount of the oxide contained in base materialis too low so that in some regions the base material's crystal becomescoarser in a location dependent manner. In the case of exceeding 1%, thecontribution to electrochemical reaction becomes larger, therebyaffecting analysis data and deteriorating the machinability. In the caseof machining the electrode into a shape for which drawing-workabilityand malleability are required, it is preferable to set the dispersedparticle concentration at 0.01 to 0.15% in order to enhance themachinability.

It is not always necessary for all the additive metal in the basematerial to be in the state of an oxide. For example, as a manufacturingmethod of the metal oxide dispersion type composite material there isthe one that forms dispersed particles by oxidizing an addedmetal-holding platinum powder and then oxidizing added metals; however,in this case, all added metals are not strictly required to be convertedto oxides in the oxidation processing—what is required is that arequisite quantity of dispersed particles are finely dispersed therein.To lessen the influence on the electrochemical reaction, it ispreferable to sufficiently perform the oxidation treatment.

Although the shape of the composite material of the metal oxidedispersion type of the present invention is not specifically limited toa wire-like shape, a rod-like shape, a mesh-like shape, or the like, theone that has a plate-like shape formed by rolling treatment or the likeis particularly good; preferably employable is the one that is enhancedin the crystal orientation property of composite material by executionof strong rolling during cold rolling.

The metal oxide-dispersed composite material is manufacturable by knownmethods.

An exemplary method is as follows. After having formed a platinum alloywith zirconium added to platinum, a platinum alloy powder is formed bythe so-called flame spray coating method, which fuses and sprays theplatinum alloy into water with a flame gun or the like, thereby forminga platinum alloy powder. This platinum alloy powder undergoes oxidationin an atmosphere of the air of high temperature. The oxidized platinumalloy powder is then subjected to compression molding to have aprescribed shape; thereafter, sintering is performed at hightemperatures. The resultant molded body is applied shape-machining usingan air hummer, cold rolling, and heating treatment forrecrystallization.

Another method is as follows. Powder preparation-completed platinum isprovided; then, chemical precipitation reaction is utilized to formzirconium hydroxide-supporting platinum which supports zirconiumhydroxide. By using a powder of this zirconium hydroxide-supportingplatinum, molding, sintering, forging, cold rolling, and heating forrecrystallization are sequentially performed. To disperse the metaloxide uniformly in the finally completed product, it is preferable thatthe particle size of platinum powder of a starting material be set in arange of 0.05 to 10 μm.

Still another method is as follows. A platinum powder in the state thata zirconium oxide is supported in platinum is formed by coprecipitationmethod and this platinum powder is used to manufacture the compositematerial. Namely, a hexachloroplatinic acid solution and zirconiumnitrate solution are mixed together; then, adding hydrazinehydrate as areducing agent and calcium hydroxide as a pH regulator thereto causescoprecipitation reaction to take place, thus obtaining aplatinum-zirconium hydroxide powder. Thereafter, percolation,desiccation, and sintering are performed to obtain the powder ofzirconium oxide-holding platinum. Then, sintering, forging, coldrolling, and recrystallization are performed sequentially.

In the crystal orientation ratio of electrode surface, the metaloxide-dispersed composite material of the present invention ispreferably arranged so that one of a plurality of crystal directions isoriented preferentially. The crystal orientation ratio of the electrodesurface is defined by the following Equation (1).(Orientation Ratio of Crystal Direction)=I(hkl)/ΣI(hkl)×100  (1)where I(hkl) is the diffraction intensity integration value of each faceobtained by X-ray diffraction measurement of the electrode surface, andΣI(hkl) is a total sum of diffraction intensity integration values of(hkl). Note here that in this description, the preferential orientationproperty is calculated from a diffraction intensity integration value ofeach of the (111) plane, the (200) plane, the (220) plane, and the (311)plane obtained by X-ray diffraction measurement, in accordance withEquation (1) presented above.

Although the preferable plane direction is not specifically limited, ametal oxide-dispersed composite material with any one of the (111),(200), (220), and (311) planes being preferentially oriented in theX-ray diffraction of the electrode surface is preferable. An electrodewith a prescribed plane direction occupying 80% or more in peakintegration value is preferable; more preferable is a material with the(220) plane's orientation ratio showing 80%. To that end, it ispreferable to perform the cold rolling under the condition of the draftbeing set at 70% or greater—preferably, 90% or more—and further applymechanical polishing and electrolytic polishing to the surface ofresultant material as will be set forth later. Incidentally, the draftis defined by Equation (2) below.(Draft)=(t ₀ −t)/t ₀×100  (2)where in Equation (2) above, t₀ is the thickness before rolling, and tis the thickness after rolling.

The material of a lead wire connected to the metal oxide-dispersedcomposite material may be a widely used metallic material low inelectrical resistance, such as copper, aluminum, silver, or platinum, ormay be a wiring lead made of any one of such metals with its surfacebeing dielectrically coated, although not specifically limited thereto.The connection between such the lead wire and the dispersion typecomposite material is achievable by known methods such as welding orsoldering.

On occasions when defining the electrode area or when wanting to preventeither the lead wire material or a contact portion from being immersedin a liquid sample, it may be embedded in insulative resin except forpart of the electrode surface. The insulative resin may be superior inchemical resistant such as fluorinated resin, polyethylene,polypropylene, polyester, polyvinyl chloride, epoxy resin,polyether-ether-ketone, polyimide, polyamide-imide, polystyrene,polysulfone, polyether sulfone, polyphenylene sulfide, and acrylic resinand also can be adequately chosen in accordance with a liquid sample asthe analyte although it is not particularly limited to.

The electrode of the present invention may be fastened to an insulativesubstrate by using an adhesive agent. The insulative substrate may bemade of a material similar to that of the above-stated insulative resin.A resin material with thermoplasticity, thermalsetting, orphotohardening such as an epoxy-based or acrylic substance may be usedas the adhesive agent; it is not specifically limited thereto and may beproperly chosen as long as it is excellent in chemical resistancesimilar to the insulative resin.

In a case where the electrode is buried in an insulative resin or fixedto an insulative substrate, a clad material with another metal beingdisposed as an underlayer of the electrode of the present invention isusable. For example, a material in which the metal oxide-dispersedcomposite material and a valve metal such as titanium are adhered witheach other may be used. As for the adhesion, it is needed to quicklyadhere with platinum while exposing the metal surface of titaniumbecause the surface of titanium or the like reacts with oxygen, carbon,nitrogen, and the like to form an inactive coating. To do this, forexample, the inactive coating formed on the titanium surface is removedby etching or the like in a vacuum and, thereafter, it is forged whilebeing contacted with the composite material, thereby enabling theadhesion. It is also possible to perform cold rolling after having thetitanium and the metal oxide-dispersed composite material joinedtogether by known explosive welding methods. It is more preferable toform it by contacting together the cold rolled metal oxide-dispersedcomposite material and the titanium having its surface platinum-platedand then applying forging thereto. In the case of applying the platinumplating to the titanium surface, surface may be treated with asandblasting method or a chemical etching method as pretreatment foradhesiveness improvement. In the chemical etching method, there may beused a hydrofluoric acid, fluoride-containing hydrofluoric acid,concentrated sulfuric acid, hydrochloric acid, oxalic acid, or a mixedsolution of them.

The plate thickness of underlayer metal is preferably 0.01 to 5 mm froma viewpoint of machinability of bending, cutting, or the like althoughnot specifically limited thereto. The plate thickness of the metaloxide-dispersed composite material is preferably 0.01 to 0.3 mm. Morepreferably, it ranges from 0.02 to 0.15 mm. Under the influence of localheat and pressure concentration in the rolling process, a state ofcrystalline texture different from the inside may be formed in a topsurface layer, the depth of which may reach about 0.01 mm from thesurface layer according to circumstances. Due to this, it is preferableto set the thickness of metal oxide-dispersed composite material to 0.01mm or greater and to use it while exposing the internal crystallinetexture to the top surface after removal of the surface layer bymechanical polishing. When the thickness is 0.3 mm or more, the amountof platinum becomes greater, resulting in an increase in cost.

The metal oxide-dispersed composite material is preferably arranged sothat its surface is mechanically polished as stated above. Moreover, itis preferable that electrolytic polishing is carried out after themechanical polishing. Regarding the electrolytic polishing it ispreferable to iteratively apply electrical potential between ahydrogen-producing region and an oxygen-producing region in anelectrolytic solution that contains an acid or a strong alkali componentsuch as potassium hydroxide. As for the waveform of the appliedpotential, a triangular waveform, a rectangular waveform, or the likemay be used although there is no particular need to limit thereto in thepresent invention.

The aforementioned mechanical polishing and electrolytic polishing areparticularly effective in the case of performing cold rolling treatmentunder the condition of a large draft. Namely, it was revealed that thecrystal orientation property near the surface of a material formedthrough the rolling treatment inter alia is relatively random and localsurface heating causes differences in crystal grain diameter and inorientation between the plate inside and its surface layer part. While asurface alteration layer formed by rolling is removed to some extent inthe material after being mechanically polished, a surface alterationlayer formed by pressurization during mechanical polishing and scarscaused by abrasive particles still exist still. Also in themanufacturing method of the present invention, the cold rolling allowsthe inside of platinum to be in the state that it has crystalorientation property; however, it is conceivable that a surfacealteration layer with irregular crystal orientation is formed. Themechanical polishing and electrolytic polishing are effective on removalof the aforementioned surface alteration layer, and can be said to bethe process for exposing the material's internal part having highcrystal orientation property.

As previously stated, according to investigation of the etching behaviorof platinum surface, step-like differences take place in units ofcrystal direction-different textures due to a change in etching ratedepending on the surface's crystal direction. Furthermore, when acrystal layer which can be seen by cross-section observation of theplatinum in the plate thickness direction exceeds 5 μm, analysisiteration, that is, progression of etching, causes the electrodesurface's unevenness to become prominent, resulting in variation of theelectrode surface area.

Especially, in the case of a working electrode being placed in a flowcell, if such unevenness of the electrode surface is significant, astable liquid flow can no longer be secured, leading to a failure tosufficiently perform the fluid replacement of an analyte liquid and acleaning fluid, and resulting in the lack of an ability to performproper analysis.

Consequently, it is also conceivable to lessen the crystal layer tothereby suppress large variation of the electrode surface area. Namely,in order to stabilize analysis data over a long time, it is effective toperform etching uniformly in the plate thickness direction while settingthe thickness of platinum crystal layer to 5 μm or less, preferably 3 μmor less, more preferably 1 μm or less.

In short, in the electrode for electrochemical measurement to be used inan electrochemical analysis apparatus which measures electrochemicalresponse of a chemical component contained in a liquid sample, a valvemetal of any of Ti, Ta, Nb, Zr, Hf, V, Mo, and W and platinum arelaminated with each other, a cross-sectional crystal texture of theplatinum part in the plate thickness direction is formed in a layer-likeform with respect to the surface of the electrode, and the thickness ofeach layer of the platinum part is made to 5 μm or less.

However, the thickness of each layer is preferably set to 0.01 μm orgreater since excessive miniaturization of crystal grains causes thematerial to become harder, resulting in degradation of theprocessability. The term “layered crystal texture” as used herein refersto the state that the individual crystal texture is elongated withrespect to a direction along the electrode plane, that is, stretched inthe rolling direction and the state of being compressed in the electrodeplate thickness direction. Also, it should be noted that the individuallayer is not meant to consist of a single crystal structure;substantially, it consists of a plurality of differently elongatedcrystal textures. The term “thickness of crystal layer” denotes thelength of individual crystal of the platinum part in the plate thicknessdirection, which can be seen when observing the through-thicknesscross-section of a layered electrode of platinum and valve metal.

Incidentally, the individual crystal refers to the texture surrounded bya small-tilt grain boundary with its grain boundary angle of less than 2degrees. A crystal texture image is observable by electron beambackscatter pattern methods or the like.

For the reason stated above, control of the crystal orientation propertyof electrode surface as well as the thickness of platinum crystal layeris effective for improvement of the analysis data stability. Apreferable plane direction is not specifically limited thereto;electrode with any one of the (111) plane, the (200) plane, the (220)plane, and the (311) plane being preferentially oriented in the X-raydiffraction of platinum surface is preferred. Preferably used isplatinum with a prescribed plane direction occupying 80% or more in apeak integration value.

More preferably usable is platinum with its (220) direction beingoriented preferentially, which is obtained by fabrication using hotrolling, annealing, and cold rolling in combination. To set thethickness of platinum layer to 5 μm or less, it is performed under thecondition that the draft is at 70% or more—preferably, 90% or more—inthe process of cold rolling at temperatures lower than or equal to theplatinum's recrystallization temperature.

As stated above, concerning the adhesion with the valve metal such astitanium, the surface of titanium or the like reacts with oxygen,carbon, nitrogen, and the like thereby to form an inactive coating and,therefore, it is necessary to expose the metal surface of titanium andto have it rapidly adhere with the platinum. To this end, for example,the inactive coating formed on the titanium surface is removed away bydry etching or the like in a vacuum; thereafter, let it abut on aplatinum plate and then undergo forge-welding at temperatures lower thanthe platinum's recrystallization temperature, thus enabling fabricationof the adhesion.

Alternatively, it is also possible to perform cold rolling after havingwelded the titanium and the platinum together by known explosive weldingmethods. It is also permissible to make a cold rolled platinum foil anda titanium plate adhere with each other by explosive welding methods.

Still alternatively, it is also possible to fabricate by joiningtogether a cold rolled platinum foil and a titanium having its surfaceplatinum-plated with their platinum surfaces oppose each other and thenperforming forging at temperatures lower than the recrystallizationtemperature. In the case of applying platinum plating to the titaniumsurface, surface may be treated with a sandblasting method or a chemicaletching method as pretreatment for adhesiveness improvement. In thechemical etching method, there may be used a hydrofluoric acid,fluoride-containing hydrofluoric acid, concentrated sulfuric acid,hydrochloric acid, oxalic acid, or a mixed solution of them.

An electrode having a platinum-plated valve metal is also usable. Withthe control of crystal grain size and orientation property, the platinumplating is enabled by controlling the current density in a plating fluidthat contains an organic material as an additive agent. Further, it isalso possible to adjust the thickness of platinum crystal layer and thecrystal orientation property by performing, after the plating, rollingtreatment at temperatures below the recrystallization temperature.

The plate thickness of the valve metal as an underlayer electrode of themultilayer electrode is preferably set at 10 to 5000 μm from a viewpointof machinability of bending, cutting, or the like although notspecifically limited thereto. The thickness of platinum part of themultilayer electrode is preferably 10 to 150 μm. More preferably, themultiplayer electrode's platinum part thickness is 20 to 100 μm.

In the rolling process, a layer having random crystal orientationproperty may be formed on the top surface layer or a coarse crystaltexture is formed due to heat concentration, the depths of which reachabout 10 μm from the top layer depending on circumstances. In view ofthis, the thickness of platinum part is preferably arranged to exceed 10μm. With a thickness of 150 μm or greater, the amount of platinumbecomes larger, resulting in an increase in cost, although it ispossible to secure a mechanical strength enough to have no trouble withthe electrode being handled alone. Setting the platinum part thicknessto 100 μm makes it possible to reduce the platinum amount to therebylower the cost and to have sufficient mechanical strength free fromhandling problems because of the multilayer electrode structure.

Preferably, after having fabricated the multilayer electrode byunification of the platinum and the valve metal, mechanical polishing isapplied to the platinum electrode surface in a similar way to the eventwhere the metal oxide-dispersed composite material is used. Morepreferably, the mechanically polished electrode is further subjected toelectrolytic polishing.

As with the case of the metal oxide-dispersed composite material beingused, the above-stated mechanical polishing and electrolytic polishingare effective processes, especially in the multilayer electrode ofplatinum and valve metal which was formed by rolling or explosivewelding method. Namely, it has been revealed that the crystalorientation property near the surface of an electrode which specificallyhas experienced hot rolling treatment is relatively random or theplate's inner part and its surface layer part are different from eachother in crystal grain size and in orientation property due to localsurface heating. While a surface alteration layer formed by such rollingis removed to some extent for the mechanically polished electrode, therestill exist the influence of pressure application during the mechanicalpolishing and scars caused by abrasive particles.

In this manufacturing method of the present invention, the cold rollingcauses the inner part of platinum to have crystal orientation propertyas well; however, it is considered that a surface alteration layer withirregular crystal orientation property is formed near the surface. Thisis similar to the case of using the metal oxide-dispersed compositematerial in that the electrolytic polishing is effective on removal ofthe aforementioned surface alteration layer and can be said to be theprocess for exposing the metal inside's platinum part having highcrystal orientation property.

To determine the degree of removal of the alteration layer on thematerial surface in the electrode manufacturing process, it ispreferable to immerse the above-stated electrode in a prescribedelectrolysis solution during electrolytic polishing and diagnose itssurface state by means of cyclic voltammetry. Namely, from the resultsof this cyclic voltammetry a plurality of hydrogen absorption/desorptioncurrent peaks can be obtained. These current peaks become currentamounts depending on the plane directions of the electrode surface andthus may serve as the criterion for determining the degree of removal ofa surface alteration layer created by rolling and mirror-polishingprocesses.

Areas of at least two of the obtained peaks are calculated along with anarea ratio thereof. Based on such calculation results, electrolyticpolishing is carried out until a prescribed area ratio is reached,thereby making it possible to obtain the electrode with the surfacealteration layer removed away.

Incidentally, examples of the electrolytic solution used in the cyclicvoltammetry include sulfuric acid, phosphoric acid, hydrochloric acid,perchloric acid, sodium hydroxide, potassium hydroxide, and aqueousammonia.

A counter electrode for use in an electrolysis cell may be appropriatelychosen in accordance with the liquid sample under analysis; platinum ora platinum alloy is employable. The electrode of the present inventionmay also be used as the counter electrode. Examples of its shapeinclude, but not limited to, a wire-like shape, a rod-like shape, amesh-like shape, and a plate-like shape.

A reference electrode used in an electrolysis cell may be asilver|silver-chloride electrode, a saturated calomel electrode, asilver electrode, or the like, although not specifically limitedthereto.

It was revealed that the electrolysis cell and an analysis apparatususing the above-stated metal oxide-dispersed composite material as theirworking electrodes are such that their electrochemical responses areless in variation of electrode surface state over an extended period oftime and also less in change in exposed crystal orientation property,thus showing stable measurement results. In the case of placing theworking electrode in a flow cell, it also becomes possible to suppressformation of the electrode surface state—in particular, local dents inthe electrode plane—for a prolonged time period to thereby stablyperform the liquid substitution of an analyte liquid and a cleaningfluid, resulting in improvement of data stability.

It was also found that the analysis apparatus using as its workingelectrode the above-stated electrode with platinum and valve metalunified and multilayered is less in variation of electrochemicalresponse over a long time and exhibits stable measurement results. Inthe case of placing the working electrode in a flow cell, the electrodeis also less in variation of its surface area over a long time and alsoless in variation of surface irregularity; thus, it becomes possible tostably implement the substitution of an analyte liquid and a cleaningfluid, resulting in improvement of data stability.

Additionally, in the electrochemical analysis apparatus including theflow cell, when using as the working electrode an electrode that wasformed by a manufacturing process including rolling treatment, it ispreferable to place it in such a manner that the electrode's rollingdirection forms an angle with the flow direction of a liquid sample of45 to 135 degrees. Regarding the analytic substance, in the case ofanalyzing the electrochemical response of a chemical component adsorbed,for example, to magnetic beads or the like, if the rolling direction isthe same as the flowing direction, then the beads tend to readily flowfrom the working electrode while being analyzed, resulting that datatend to vary. In cases where the rolling direction is less than 45degrees or exceeds 135 degrees with respect to the flow direction, theaforementioned influence can take place in no small extent. It was foundthat when the electrode is disposed so that the rolling direction fallswithin a range of 45 to 135 degrees with respect to the flow directionin angle, a step produced between crystal textures thereof—though thisis tiny irregularity—causes magnetic beads with their sizes ofsubmicrons to several μm, for example, to easily reside on the workingelectrode surface, resulting in an ability to improve the datastability.

By using the electrode, the electrolysis cell, and the electrochemicalanalysis apparatus of the present invention, it is possible to analyze achemical component contained in a liquid sample such as blood, urine, orthe like, examples of which component are shown below.

That is to say, some of such examples are glucose, glycosylatedhemoglobin, glycosylated albumin, lactic acid, uric acid, urea,creatinine, bile acid, cholesterol, neutral fat, ammonia, urea nitrogen,bilirubin, and histamine. Note, however, that these are not limitedthereto as far as they are components which exhibit the electrochemicalresponse of redox species occurred by the action of enzyme, mediator, orthe like. Also analyzable are components to be subjected toelectrochemical measurement after having captured the target componenton the electrode surface using magnetic particles having their surfacesmodified by a component selectively connecting with the chemicalcomponent being analyzed.

On occasions when detecting the glucose, the concentration of it isquantitatively determined by on-electrode reduction or oxidation ofhydrogen peroxide, which was produced by letting glucose oxidase actthereon by way of example.

When detecting the glycosylated protein such as glycosylated hemoglobinor glycosylated albumin, it is possible to quantify the concentration ofglycosylated protein by releasing glycosylated peptide from theglycosylated protein with protease, for example, and then reducing oroxidizing on the electrode a hydrogen peroxide which was produced byletting glycosylated peptide oxidase act thereon.

When detecting the lactic acid, its concentration is quantifiable, forexample, by reducing or oxidizing on the electrode a hydrogen peroxidethat was produced by letting lactate oxidase act thereon.

When detecting the uric acid, its concentration is quantifiable, forexample, by reducing or oxidizing on the electrode a hydrogen peroxideproduced by letting uricase act thereon.

When detecting the urea, its concentration is quantifiable, for example,by oxidizing on the electrode a potassium ferrocyanide produced bycausing glutamate dehydrogenase to act on ammonia produced by lettingurease act thereon, in the presence of β-nicotinamide adeninedinucleotide (NADH) and potassium ferricyanide.

When detecting the creatinine, its concentration is quantifiable, forexample, by reducing or oxidizing on the electrode a hydrogen peroxidethat was produced by causing creatininase, creatinase, and sarcosineoxidase to act thereon sequentially.

When detecting the bile acid, its concentration is quantifiable, forexample, by oxidizing on the electrode a potassium ferrocyanide that wasproduced by causing bile-acid sulfuric-acid sulfatase andβ-hydroxysteriod dehydrogenase to sequentially act thereon in thepresence of reduction-type NADH and potassium ferricyanide.

When detecting the cholesterol, its concentration is quantifiable, forexample, by reducing or oxidizing on the electrode a hydrogen peroxideproduced by letting cholesterol oxidase act thereon.

When detecting the neutral fat, its concentration is quantifiable, forexample, by reducing or oxidizing on the electrode a hydrogen peroxideproduced by letting glycerophosphate oxidase act thereon.

When detecting fatty acid, its concentration is quantifiable, forexample, by reducing or oxidizing on the electrode a hydrogen peroxideproduced by letting acyl-CoA oxidase act thereon.

When detecting the ammonia, its concentration is quantifiable, forexample, by oxidizing on the electrode a potassium ferrocyanide producedby letting glutamate dehydrogenase act thereon in the presence of NADHand potassium ferricyanide.

When detecting the bilirubin, the concentration of urea nitrogen isquantifiable, for example, by oxidizing on the electrode a potassiumferrocyanide that was produced by letting bilirubin oxidase act thereonin the presence of potassium ferricyanide.

The above-described enzyme and the like are immobilized on a surface ofthe electrode. Examples of the methodology of fixing the enzyme and thelike to the electrode surface include, but not limited to, a method forimmersing the electrode in either an aqueous solution of the enzyme andthe like or a buffer fluid and a method of causing an aqueous solutionof the enzyme and the like or a buffer fluid to fall onto the electrodeto thereby immobilize the enzyme physically or chemically. Anotherexample is a method for immersing the electrode in a solution containingthiol with a functional group such as a carboxyl group or an amino groupintroduced into the end group so that aforementioned thiol is adsorbedonto the electrode surface and then for letting the enzyme or the likereact therewith to thereby perform immobilization. Further examples area method for immobilizing the enzyme or the like on the electrode byusing either a cross-linking reagent such as glutaraldehyde or byfurther using bovine serum albumin, a method for forming on theelectrode a film of gel such as hydrophilic macromolecules and thenfixing the enzyme or the like in this film, and a method for forming onthe electrode an conductive polymeric film such as polythiophene andthen fixing the enzyme or the like therein.

Upon detection of the object to be analyzed, it is effective to utilizemediator molecules, as the need arises, in order to extend the range ofdetected concentration. In the case of using mediator molecules, it ispreferable to place the mediator molecules on the electrode in animmobilization film of biologically active substance of the enzyme andthe like formed on the electrode or separately therefrom. Kinds of themediator molecule include are not particularly limited but at least oneof potassium ferricyanide, potassium ferrocyanide, ferrocene and itsderivative, viologen and the like, methylene-blue, and the like can beused.

Next, an explanation will be given of embodiments of the presentinvention based on the above-stated principles.

Embodiment 1

Explained below is an overall arrangement of an electrochemical analysisapparatus in accordance with one embodiment of the present inventionusing an electrode in accordance with one embodiment of this invention.

FIG. 1 shows an entire configuration of an electrochemical analysisapparatus in accordance with Embodiment 1 of the present invention.Embodiment 1 of this invention is an electrochemical analyzer having theform of a batch processing scheme.

In FIG. 1, an electrolysis cell 1 has a working electrode 2, a counterelectrode 3, and a reference electrode 4 which are disposed therein.Respective electrodes 2, 3, 4 are connected by lead wires 7 to anelectric potential-applying means 5 and a measuring means 6. The counterelectrode 3 used here is the one that was obtained by rolling platinuminto a plate-like shape and then mechanically polishing its surface. Thereference electrode 4 was an Ag|AgCl electrode. Note here that in thisdescription, the silver|silver-chloride (saturated potassium chlorideaqueous solution) electrode is denoted by Ag|AgCl.

A solution-dispensing mechanism 11 introduces into a solution inlet pipe13 an analyte solution that contains a chemical component undermeasurement from an analyte solution vessel 8 and a buffer fluid from abuffer fluid vessel 9, respectively. The solution under measurement andthe buffer fluid thus introduced are mixed together in the solutioninlet pipe 13 and the mixed solution is injected by a solution injectionmechanism 12 into the electrolysis cell 1, thereby performingelectrochemical measurement of the object to be assayed.

As for the potential applying means 5 a potentiostat, a galvanostat, aDC power supply, an AC power supply, or a system with one of them beingconnected to a function generator or the like can be used. The measuringmeans 6 measures electrochemical characteristics of the object assayed.Incidentally, the electrochemical characteristics may be any one ofknown measurement schemes such as potentiometry, amperometry,voltammetry, and impedance measurement although not specifically limitedthereto. Others include a method for detecting, by an optical element,photons to be produced in accordance with electrochemical reaction.

The measurement-completed solution is sucked by a solution exhaustmechanism 15 and then discarded to a waste container 16 through asolution outlet pipe 14. After completion of the measurement of asample, a cleaning liquid is inhaled by the solution-dispensingmechanism 11 from a cleaning liquid vessel 10 and then supplied by thesolution injection mechanism 12 into the electrolysis cell 1. Thecleaning liquid that rinsed the interior of the electrolysis cell 1 isdiscarded to the waste container 16.

Here, as a typical example, the voltage applying means 5 outputs to theworking electrode during measurement of the to-be-measured solution avoltage having a pulse-like waveform with positive and negativepotentials being repeated in a prescribed cycle. This pulse-likewaveform potential is arranged to be applied on occasions whencontinuously flowing in the electrolysis cell a measurement solutionthat contains large amounts of protein and halogen element such as bloodfor a long time period or when flowing a cleaning agent of a strongalkali such as potassium hydroxide into the measurement vessel. Althoughin this Embodiment 1 the above-noted potential application waveform wasused, this invention is not specifically limited thereto.

Here, an electrode material used for the working electrode 2 is acomposite material with zirconium oxide being dispersed in platinum. Theaforementioned composite material was fabricated in accordance with afabrication method which follows. A platinum-0.2% zirconium alloy wassubjected to vacuum fusion, thus forming an ingot. Subsequently, afterforging treatment, the aforementioned ingot was rolled to therebyperform wiredrawing processing. This wiredrawn one was fused and sprayedby a flame gun toward a distilled water bath, thereby obtaining aplatinum alloy powder. The obtained platinum alloy powder was held inthe air at 1250° C. for 24 hours; then, oxidation processing was appliedthereto. The oxidized alloy powder is temporarily sintered at 1250° C.and then molded and solidified by a hot press. To improve the degree ofcompactness, the molded body is subject to hot forging. Finally, thisalloy was cold rolled with a draft of 90% and heated at 1400° C. for 1hour, thereby obtaining a plate-shaped composite material with a platethickness of 0.2 mm.

The above-stated composite material was used to fabricate the workingelectrode 2 in a procedure which follows.

The aforementioned composite material was cut into a size of 5 mm indiameter. Thereafter, by a working electrode manufacturing apparatus 50shown in FIG. 2, a lead wire 302 was first connected by soldering to theback surface of composite material 301 that has been cut at anelectroding unit 50 a. A dielectric resin-coated copper line was used asthe lead wire.

Next, at a resin embedding unit 50 b, an adhesive agent 303 was used toembed it in an insulative resin 300 in such a way that only thecomposite electrode's surface is exposed at a portion having a circularshape with a diameter of 5 mm. As the dielectric resin, a fluorine-basedresin was used.

Next, at a mechanical polishing unit 50 c, the electrode surface wasmechanically polished by sequentially using water-proof abrasive paper,diamond paste, and alumina particles, thereby causing it to have amirror-finished surface.

Next, a stainless-steel shaft 304 was screwed into the fluorine-basedresin, thereby connecting the shaft 304 and the lead wire 302 with eachother. Finally, at an electrolytic polishing unit 50 d, electricalpotential scanning was repeated 10,000 times between potential levels of−1.2 to 1.0V vs. Ag|AgCl in a 0.2 mol/L potassium hydrate aqueoussolution at a potential scanning rate of 0.1 V/s, thus obtaining theworking electrode 2 shown in FIG. 3. Note that FIG. 4 is a schematiccross-sectional diagram taken along line A-A′ of FIG. 3.

X-ray diffraction measurement was performed of the electrode surface ofthe working electrode 2 fabricated in the present Embodiment 1. CuKα wasused as an X-ray source to measure three different points on theelectrode surface with output settings of 40 kV and 20 mA. Integrationvalues (I) of diffraction peaks of a (111) plane, a (200) plane, a (220)plane, and a (311) plane on the platinum surface were calculated tothereby obtain each direction's orientation ratio((%)=I(hkl)/ΣI(hkl)×100). Incidentally, the calculation of each peakintegration value was done in the ranges of 37°≦2θ≦42° for the (111)plane, 44°≦2θ≦49° for the (200) plane, 65°≦2θ≦70° for the (220) plane,78°≦2θ≦83° for the (311) plane, respectively (where θ is the diffractionangle). As results of the measurement, as shown in FIG. 5, it wasrevealed that the plane index (220) is preferentially oriented with itsorientation ratio of 95%.

FIG. 6 is a diagram for explanation of the effect of a metaloxide-distributed platinum electrode employed in Embodiment 1 of thepresent invention. Measurement was repeatedly performed with TSH(thyroid stimulating hormone) of the same concentration as an analyte.The abscissa of FIG. 6 designates the number of times of testing whereasthe ordinate indicates the value of each actual measurement valuedivided by a reference value. The reference value is an output valueupon measurement of a TSH-containing solution with a prescribedconcentration; the actual measurement values are measured values whenrespective solutions used in Embodiment 1 and Comparative Example 1. Thevariation range is defined as a difference between values obtained inthe sixty-thousandth test and in the first test. In FIG. 6, linesconnecting circular marks are in the case of this Embodiment 1 and lineconnecting triangular marks are in the case of Comparative Example 1different from the present invention.

The electrode of FIG. 3 and the electrochemical analyzer of FIG. 1 wereused to perform measurement in a method for immunologically analyzing aTSH in blood serum as the measurement solution and for introducingpotassium hydroxide aqueous solution, for example, as a cleaning liquidinto the electrolysis cell once per completion of each measurement.

As shown in FIG. 6, the variation range in the case of using anelectrode of Comparative Example 1 was 10.3%. The electrode ofComparative Example 1 is a platinum electrode to which hot rolling andrecrystallization processing were applied and to a platinum surface ofwhich mechanical polishing and electrolytic treatment were applied.Details will be explained in the context of comparative examples to bedescribed later. On the other hand, in the case of using the electrodeof the present Embodiment 1, the variation range was reduced to 4.2%.

The electrode of this Embodiment 1 is a platinum electrode in whichzirconium oxide was dispersed as a metal oxide. The contained amount ofzirconium in this electrode is 0.2% in the metal-equivalent value,wherein a surface alteration layer that was created during the rollingand mechanical polishing processes is removed away and wherein it ispreferentially oriented in the plane direction (220) at an orientationratio of 80% or more. In the analyzer using this electrode as itsworking electrode, the etching rate difference within the electrodesurface is small so that advantageous effects were ascertained thatnon-uniform in-plane dissolution is suppressed and the crystalorientation property of crystals exposed to the top surface is small inchange even when the analysis is repeated so that it becomes possible toreduce variations of the surface state and a fluctuation in theelectrochemical response is small over a long period, thus making itpossible to obtain stable measurement results.

While in Embodiment 1 the electrode with composite material buried influorine resin was used, a metal oxide-dispersed composite material isused as the electrode and this electrode exhibits an effect on the datastability. So, this invention is not specifically limited to any form.For example, it was made sure that similar effects are also obtainablein the case of a plate-like form where it is not buried in resin asshown in FIG. 7, for example (FIG. 8 is a side view of FIG. 7).

Embodiment 2

Embodiment 2 of the present invention will be set forth next. Anelectrode and an electrochemical analysis apparatus using it are similarto those of Embodiment 1 except that in the manufacture of an electrode,the electrode is immersed in a prescribed electrolysis solution duringelectrolytic polishing, and a surface alteration layer on the electrodesurface is removed while at the same time conducting diagnosis on thesurface state by cyclic voltammetry. The cyclic voltammetry wasperformed using a nitrogen-substituted phosphoric acid buffer fluid at apH of 6.86 as the electrolytic solution under the condition of apotential scan range of from −0.6 to 1.1 V and a scan rate of 0.1 V/swhile letting its working electrode be the working electrode 2, lettingits counter electrode be a platinum wire, and letting its referenceelectrode be Ag|AgCl. A measurement result is shown in FIG. 9.Incidentally, for comparison purposes, a result of Comparative Example 1is also shown. Among a plurality of hydrogen absorption/desorptioncurrent peaks obtained from the results of cyclic voltammetry, letting“a” to be a peak observed in a range of −0.37 to −0.31 V and “b” to be apeak seen in a range of −0.31 to −0.2 V, their peak areas and an arearatio b/a are calculated. Electrolytic treatment was performed until thearea ratio becomes 80% or less; thus, the working electrode 2 wasobtained.

As a result of repeated execution of analysis by the electrochemicalanalyzer using the working electrode in accordance with Embodiment 2 ofthe present invention in a similar way to Embodiment 1, an excellentresult was obtained showing that the variation range is 3.8%. As aresult of X-ray diffraction analysis of the electrode, it was revealedthat it is preferentially oriented in the (220) direction with anorientation ratio of 96%. In the analyzer using this electrode as itsworking electrode, the etching rate difference within the electrodesurface is small so that advantageous effects were ascertained thatnon-uniform in-plane dissolution is suppressed and the crystalorientation property of crystals exposed to the top surface is small inchange even when the analysis is repeated so that it becomes possible toreduce variations of the surface state and a fluctuation in theelectrochemical response is small over a long time, thus making itpossible to obtain stable measurement results.

Although in Embodiment 2 of this invention the peaks a and b are used asthe criterion for judgment of the degree of surface alteration layerremoval, it was ascertained that similar results are also obtainable bycalculating a ratio b/c from the peak c seen in the range of −0.48 to−0.37 V and the peak b and for letting b/c be 35% or less as thecriterion.

Embodiment 3

An electrochemical analysis apparatus in accordance with Embodiment 3 ofthe present invention will be explained using FIG. 10, FIG. 11A, andFIG. 11B. FIG. 10 is a schematic configuration diagram of theelectrochemical analyzer in Embodiment 3 of this invention. In addition,FIG. 11A is an exploded configuration diagram of a flow cell for use inthe electrochemical analyzer shown in FIG. 10, and FIG. 11B is itsassembly cross-section diagram.

The example shown here in FIG. 10 is similar to that shown in FIG. 1except that the electrolysis cell 1 shown in FIG. 1 is replaced with aflow cell 20 in FIG. 10.

In FIG. 11B, the flow cell 20 serving as an electrolysis cell was formedby laminating two electrically insulative substrates 30 and 32 and asealing member 31 shown in FIG. 11A in a way shown in FIG. 11B. As theinsulative substrate 30 polyether ether ketone was used. On one face ofthe insulative substrate 30, a working electrode 34 is fastened. Here,an electrode material used for the working electrode 2 was a compositematerial with zirconium oxide dispersed in platinum. The compositematerial was fabricated by a manufacturing method which follows. Asuspension liquid with platinum powder of the particle diameter of 5 μmand calcium carbonate mixed together was subjected to ball-millprocessing, this suspension was heat-treated at a high temperature of1100° C., and, after having immersed the bulk obtained by suchhigh-temperature heat-treatment into water, nitric acid treatment wasperformed. 2 kg of the obtained platinum powder was put into 4 L of purewater, thereby producing a platinum suspension liquid. This platinumsuspension was mixed with 9 g of zirconium nitrate solution and agitatedat room temperature for about 3 minutes; thereafter, 2.0 g of ammoniaaqueous solution was added for adjustment to a pH of 7.5 and filteringcollection from the mixed liquid was performed, thus obtaining azirconium hydroxide-supporting platinum powder. The collected zirconiumhydroxide-holding platinum powder was rinsed and dried at 120° C. in theatmospheric air. Subsequently, this zirconium hydroxide-holding platinumpowder was forced to pass through a sieve with an aperture size of 300μm. This zirconium hydroxide-holding platinum powder was filled into avessel and cold-molded at a pressure of 100 MPa, thereby obtaining amolded body. This molded body was sintered in the air at 1200° C. for 1hour and then forged using an air hummer, thereby obtaining a platinumingot with zirconium oxide dispersed therein. Cold rolling was appliedto this ingot in which the draft became 90%. Subsequently,recrystallization heating was performed at 1400° C. for 1 hour whereby acomposite material with a plate thickness of 150 μm was fabricated. Inthe composite material obtained, zirconium oxide was contained by about0.1% in the metal-equivalent value. Incidentally, the concentration ofzirconium contained in the composite material was assayed byinductively-coupled plasma mass spectrometry (ICP-MS) after havingresolved the material by aqua regia.

The insulative substrate 30 with the immobilized working electrode 34was fabricated in accordance with a production flow shown in FIG. 16.

At an electroding unit 51 a, an insulative resin-coated aluminum wiringlead 39 was connected by soldering to the above-stated compositematerial whereby a working electrode 34 was obtained. Next, at a resinembedding unit 51 b, it was embedded into a depression portion providedin advance in the surface of the insulative substrate 30 and, then,fixed with an adhesive agent. Thereafter, at a mechanical polishing unit51 c, mechanical polishing was performed using water-proof abrasivepaper, diamond paste, and alumina sequentially until a step-like surfacedifference between the insulative substrate 30 and the electrodedisappears, thereby obtaining a mirror-finished surface. Thereafter, atan electrolytic polishing unit 51 d, application of electrical potentialwith rectangular pulses of −1.2 V/0.5 sec and 3.0 V/1.5 sec was repeated10,000 times in 0.2 mol/L potassium hydroxide aqueous solution. Theobtained working electrode 34 has its surface with Ra (arithmetic meanroughness) of about 0.6 μm. Finally, at a cell assembling unit 51 e, anelectrolysis cell 20 was formed by laminating the seal member 31 and theinsulative substrate 32.

The insulative substrate 32 is formed by a substrate made of transparentdielectric resin. A counter electrode 35 is fixed to one surface (thesurface on the side opposing the electrically insulative substrate 30)of the insulative substrate 32. The counter electrode 35 used here isthe one that was annealed at 1000° C. for 1 hour after having machinedthe platinum into the shape of the electrode.

In the surface of the electrically insulative substrate 32, a depressionportion is formed; in this depression portion, the annealed counterelectrode 35 is buried and bonded by an adhesive agent and, then, thesurface of the counter electrode 35 was mirror-polished. Incidentally,the shape of the counter electrode 35 is not limited to the plate-likeshape and may alternatively be of a comb-like shape, a mesh-like shape,or a rod-like shape. Also, the electrode material is not limited toplatinum and may also be other platinum-group metals. The counterelectrode 35 may be made of platinum to which electrolytic polishing wasapplied after the mirror polishing in a similar manner to the workingelectrode 34.

The working electrode 34 and the counter electrode 35 are connected bysoldering to lead wires 39 and 40 prior to being embedded in theinsulative substrates 30 and 32, respectively, and the lead wires 39, 40are arranged to run through holes made in the insulative substrate 30,32.

The seal member 31 is made of fluorine-based resin and has an opening 36at its center. In the insulative substrate 30, holes 21 and 22 forcoupling with pipes 37 and 38 are formed with the working electrode 34being placed therebetween; these two holes 21 and 22 are disposed to liewithin the opening 36, thereby making it possible to take a solutioninto and out of the opening 36. The working electrode 34 and the counterelectrode 35 oppose each other via the opening 36 of the seal member 31.

At four corners of the insulative substrates 30, 32 and the seal member31, screw holes 33 are formed, through which screws are put respectivelyto cramp and fasten the insulative substrate 30, the seal member 31, andthe insulative substrate 32 together, thereby forming the flow cell 20.

In the insulative substrate 30, pipes 37 and 38 made of fluororesin arefixed and connected to a surface on the side opposite to the surface onwhich the working electrode 34 is placed. As will be described later,one of the pipes 37 and 38 is connected to a mechanism for introducing asolution under measurement or the like into the flow cell 20; the otheris used as a flow path for exhausting the measurement-completedsolution. Besides, a reference electrode (not shown in FIG. 11B) isdisposed at a pipe 38, that is a part of the solution exhaust-side pipe,and is used as a reference electrode in the event of applying apotential to the working electrode.

Incidentally, the flow cell of the present invention is not specificallylimited to the embodiment shown in FIG. 11A and FIG. 11B and may bearranged to have other arrangements. Some exemplary flow cells withother arrangements will be explained below.

FIG. 12A and FIG. 12B are diagrams showing another example of the flowcell. In FIG. 12B, a flow cell 60 is formed by laminating respectivemembers shown in FIG. 12A, that is, two electrically insulativesubstrates 70 and 72 and a seal member 71 in a manner shown in FIG. 12B.Secured to one surface of the insulative substrate 70 (the surfaceopposing the electrically insulative substrate 72) is a workingelectrode 74. A counter electrode 75 is fixed to one surface of theinsulative substrate 72 (the surface opposing the electricallyinsulative substrate 70).

The working electrode 74 and the counter electrode 75 are connected bysoldering to lead wires 79 and 80 before being embedded in theinsulative substrates 70 and 72, respectively, and the lead wires 79, 80are arranged to run through holes made in the insulative substrates 70,72, respectively.

At the center of the seal member 71 an opening 76 is formed. In theinsulative substrate 72, holes 21 and 22 for coupling with pipes 77 and78 are formed with the counter electrode 75 being positionedtherebetween; these two holes 21 and 22 are disposed to lie within theopening 76, thereby making it possible to take a solution into and outof the opening 76. The working electrode 74 and the counter electrode 75oppose each other via the opening 76 of the seal member 71.

At four corners of the insulative substrates 70, 72 and the seal member71, screw holes 73 are formed, through which screws are put respectivelyto thereby cramp and fasten the insulative substrate 70, the seal member71, and the insulative substrate 72 together, thereby forming the flowcell 60.

In the insulative substrate 72, pipes 77 and 78 made of fluororesin arefixed and connected to a surface on the opposite side to the surface onwhich the counter electrode 75 is provided. One of the pipes 77 and 78is coupled, as will be described later, to a mechanism for introducing asolution under measurement or the like into the flow cell 60; the otheris used as a flow path for exhausting the measurement-completedsolution.

Beside, a reference electrode (not shown in FIG. 12B) is placed at asolution exhaust-side pipe section and used as a reference electrodewhen applying a potential to the working electrode 74.

FIG. 13A and FIG. 13B are diagrams showing a further example of the flowcell. In FIG. 13B, a flow cell 90 is formed by laminating respectivemembers shown in FIG. 13A, that is, two electrically insulativesubstrates 100 and 102 and a seal member 101 in a manner shown in FIG.13B. Secured to one surface of the insulative substrate 100 (the surfaceopposing the electrical insulative substrate 102) is a working electrode104. A counter electrode 105 is fixed to one surface of the insulativesubstrate 102 (the surface opposing the electrical insulative substrate100).

The working electrode 104 and the counter electrode 105 are connected bysoldering to lead wires 109 and 110 before being embedded in theinsulative substrates 100 and 102, respectively, and the lead wires 109,110 are arranged to run through holes made in the insulative substrates100, 102, respectively.

An opening 106 is formed at the center of the seal member 101. The shapeof the opening 106 is a hexagon in the example shown in FIG. 13Aalthough not specifically limited thereto as far as smooth liquidsubstitution is achievable without retention of each kind of solutionsto be provided into the flow cell.

In the insulative substrate 100, holes 21 and 22 for coupling with pipes107 and 108 are formed with the working electrode 104 being locatedtherebetween; these two holes 21 and 22 are disposed to position themwithin the opening 106, thereby making it possible to take a solutioninto and out of the opening 106. The working electrode 104 and thecounter electrode 105 oppose each other via the opening 106 of the sealmember 101.

At four corners of the insulative substrates 100, 102 and the sealmember 101, screw holes 103 are formed, through which screws are putrespectively to thereby cramp and fasten the insulative substrate 100,the seal member 101, and the insulative substrate 102 together, therebyforming the flow cell 90.

In the insulative substrate 100, pipes 107 and 108 made of fluororesinare fixed and connected to a side face thereof. One of the pipes 107 and108 is coupled, as will be described later, to a mechanism forintroducing a solution under measurement or the like into the flow cell90; the other is used as a flow path for exhausting themeasurement-completed solution.

Beside, a reference electrode (not shown in FIG. 13B) is disposed at asolution exhaust-side pipe section and used as a reference electrodewhen applying a potential to the working electrode.

FIG. 14A, FIG. 14B, and FIG. 14C are diagrams showing still anotherexample of the flow cell. In FIG. 14B, a flow cell 120 is formed bylaminating respective members shown in FIG. 14A, that is, twoelectrically insulative substrates 130 and 132 and a seal member 131 ina manner shown in FIG. 14B. Secured to one surface of the insulativesubstrate 132 (the surface opposing the electrical insulative substrate130) is a counter electrode 135. At the center portion of the insulativesubstrate 130 a depression portion for disposing the working electrode134 in a manner shown in FIG. 14C and a thread 143 for an electricallyconnecting bolt 141 for enabling connection with the working electrode134.

After having the working electrode 134 adhere to the insulativesubstrate 130 using an adhesive, mechanical polishing is performed.Thereafter, the electrically connecting bolt 141 is screwed into thethread 143 via an electrically connecting plate 142. As long as theelectrically connecting plate 142 is made of soft metals with lowresistivity such as, for example, gold, tin, or aluminum, it is notspecifically limited thereto. The electrically connecting bolt 141 isconnected to a lead wire 139, thus enabling electrical connection withthe working electrode 134.

The counter electrode 135 is connected by soldering to a lead wire 140prior to being embedded in the insulative substrate 132 and the leadwire 140 is arranged to run through a hole made in the insulativesubstrate 132.

At the center of the seal member 131, an opening 136 is formed. In theinsulative substrate 132, holes 21 and 22 for coupling with pipes 137and 138 are formed while letting the counter electrode 135 lietherebetween; these two holes 21 and 22 are disposed to position themwithin the opening 136, thus making it possible to take a solution intoand out of the opening 136. The working electrode 134 and the counterelectrode 135 oppose each other via the opening 136 of the seal member131.

At four corners of the insulative substrates 130, 132 and the sealmember 131, screw holes 133 are formed, through which screws are putrespectively to thereby cramp and fasten the insulative substrate 130,the seal member 131, and the insulative substrate 132 together, therebyforming the flow cell 120.

In the insulative substrate 132, pipes 137 and 138 made of fluororesinare fixed and connected to a side face of the surface on which thecounter electrode 135 is placed. One of the pipes 137 and 138 iscoupled, as will be stated later, to a mechanism for introducing asolution under measurement or the like into the flow cell 120; the otheris for use as a flow path for exhausting the measurement-completedsolution. Besides, a reference electrode (not shown in FIG. 14B) isplaced at a solution exhaust-side pipe section and used as a referenceelectrode at the time of applying a potential to the working electrode134.

FIG. 15 is a diagram showing still another further example of the flowcell. In FIG. 15, a flow cell 180 is formed by holding a workingelectrode 194 by and between an insulative substrate 190 and aninsulative chassis 192 via O-rings 191. A plurality of screw holes 193are formed at the outer periphery of the insulative substrate 190 andthe insulative chassis 192; by running screws through the respectivescrew holes 193 and securing, the insulative substrates 190 and 192 areclamped together to thereby form the flow cell 180.

A counter electrode 195 is embedded at the center of the insulativechassis 192, providing a structure with the counter electrode 195projecting toward the inside of the flow cell 180. Pipes 197 and 198made of fluororesin are fixed and connected to the insulative chassis192. One of the pipes 197 and 198 is coupled, as will be stated later,to a mechanism for introducing a solution under measurement or the likeinto the flow cell 180; the other is for use as a flow path forexhausting the measurement-completed solution. Besides, a referenceelectrode (not shown in FIG. 15) is disposed at a solution exhaust-sidepipe section and used as a reference electrode in the event of applyinga potential to the working electrode.

The working electrode 194 and the counter electrode 195 are connected bysoldering to lead wires 199 and 200, respectively.

Next, an overall configuration of the electrochemical analyzer ofEmbodiment 3 of the present invention will be explained with referenceto FIG. 10. For components similar to those of FIG. 1, detailedexplanations are eliminated herein for purposes of avoiding redundancy.

In FIG. 10, a solution to be measured in the measurement solution vessel8 and a buffer fluid in the buffer fluid vessel 9 are sucked by thesolution-dispensing mechanism 11, mixed together in the solution inletpipe 13, and then injected into the flow cell 20. While the mixed liquidis stored in the flow cell 20, a prescribed potential is applied by thevoltage-applying means 5 to the working electrode 34 within the flowcell 20, thereby performing electrochemical measurement of the object tobe assayed. A signal obtained by electrochemical reaction at the workingelectrode 34 within the flow cell 20 is transmitted via the lead wire 7to the measuring means 6 for signal processing.

Incidentally, it is also possible to optically measure a changegenerated be an electrochemical reaction by disposing a detector abovethe substrate 32 made of transparent insulative resin.

The measurement-completed solution in the flow cell 20 is sucked by thesolution exhaust mechanism 15 and then discarded to the waste container16 through the solution outlet pipe 14.

The working electrode 34 used in Embodiment 3 is an electrode made of acomposite material with zirconium oxide dispersed in platinum providedwith electrical wiring. As a result of performing X-ray diffractionmeasurement of the electrode surface, it was revealed that the planeindex (220) is preferentially oriented with its orientation ratio of85%.

Using the flow cell of FIG. 11 and the electrochemical analyzer of FIG.10, measurement was performed by a method of analyzing as themeasurement solution a compound with TSH in blood serum being adsorbedto surfaces of magnetic particles with a diameter of 3 μm, andintroducing, for example, potassium hydroxide aqueous solution as acleaning fluid into the flow cell upon completion of each measurement.The variation range of the first and the 60,000th analyses wascalculated in a similar way to Embodiment 1 to be 5.0%. In the flow celland the analyzer using this electrode as its working electrode, theetching rate difference within the electrode surface is small so thatadvantageous effects were ascertained that non-uniform in-planedissolution is suppressed and the crystal orientation property ofcrystals exposed to the top surface is small in change even when theanalysis is repeated so that it becomes possible to reduce variations ofthe surface state and a fluctuation in the electrochemical response issmall for a long time period, thus making it possible to obtain stablemeasurement results. It was also found that it becomes possible tostably perform liquid substitution of an analyte liquid and a cleaningfluid, thereby a variation in the electrochemical response being madesmall for a long time and enabling to obtain stable measurement results.It was further found that pits produced in the surface stabilizemagnetic particles of the electrode surface so that stable measurementresults are obtainable.

Embodiment 4

Embodiment 4 of the present invention will be explained. In Embodiment4, iterative measurement was performed in a similar way to Embodiment 1except that glucose of a known concentration was used as the analyte,enzyme was immobilized on the electrode surface of Embodiment 1, and themetal oxide dispersed in platinum was niobium oxide. The content of themetal oxide dispersed in platinum was 0.06% in the metal-equivalentvalue.

As a result of measurement, as shown in FIG. 17, it was found that theobtained variation range between the first and the 60,000th analyses was4.0%, which is less than that of Comparative Example 2. This ascertainedadvantageous effects that in the analyzer using the present electrode asits working electrode, the etching rate difference within the electrodesurface is small so that non-uniform in-plane dissolution is suppressed,and the crystal orientation property of crystals exposed to the topsurface is small in change even when the analysis is repeated, therebyit becomes possible to suppress surface state variations, resulting inachievement of an ability to stably control the amount of enzymemodifying on the electrode surface, and it becomes possible to stablyperform liquid substitution of an analyte liquid and a cleaning fluid,thereby a variation in the electrochemical response being made small fora long time period and enabling to obtain stable measurement results.

Embodiment 5

Embodiment 5 of the present invention will be explained. In Embodiment5, iterative analytical measurement was performed pursuant to themeasurement method of Embodiment 1 except that urea of a knownconcentration was used as the analyte and that the metal oxide dispersedin platinum was tantalum oxide. The content of the metal oxide dispersedin platinum was 0.08% in the metal-equivalent value. In the measurementsolution vessel 8, an analyte sample was caused to be acted on withurease, next with β-nicotinamide adenine dinucleotide (NADH), and thenwith glutamate dehydrogenase in the presence of potassium ferricyanide,thereby producing potassium ferrocyanide. A solution under measurementcontaining potassium ferrocyanide from the measurement solution vessel 8and a buffer fluid from the buffer fluid vessel 9 were introduced intothe solution inlet pipe 13 to be mixed together and injected into theelectrolysis cell 1 by the solution injection mechanism 12 so thatelectrochemical measurement was performed. As a result of execution ofthe iterative measurement, as shown in FIG. 17, it was found that theobtained variation range between the first and the 60,000th analyses was2.5%, which is less than that of Comparative Example 3. This ascertainedadvantageous effects that in the analyzer using the present electrode asits working electrode, etching rate difference within the electrodesurface is small so that non-uniform in-plane dissolution is suppressed,and the crystal orientation property of crystals exposed to the topsurface is small in change even when the analysis is repeated, therebyit becomes possible to suppress surface state variations, and it becomespossible to stably perform liquid substitution of an analyte liquid anda cleaning fluid, thereby a variation in the electrochemical responsebeing made small for a long time, and enabling to obtain stablemeasurement results.

Embodiment 6

Embodiment 6 of the present invention will be explained. In Embodiment6, iterative analytical measurement was performed pursuant to themeasurement method of Embodiment 5 except that cholesterol of a knownconcentration was used as the analyte, that the base metal was an alloyof platinum and 2% gold, and that the metal oxide dispersed in the basematerial was zirconium oxide. The content of the metal oxide dispersedin the base material was 0.1% in the metal-equivalent value. In themeasurement solution vessel 8, an analyte sample was caused to be actedon with cholesterol oxidase, thereby producing hydrogen peroxide. Asolution under measurement containing hydrogen peroxide from themeasurement solution vessel 8 and a buffer fluid from the buffer fluidvessel 9 were introduced into the solution inlet pipe 13 to be mixedtogether and injected into the electrolysis cell 1 by the solutioninjection mechanism 12 so that electrochemical measurement was done. Asa result of repeated execution of the measurement, as shown in FIG. 17,it was found that the obtained variation range between the first and the60,000th analyses was 5.0%, which is less than that of ComparativeExample 4. This ascertained advantageous effects that in the analyzerusing the present electrode as its working electrode, etching ratedifference within the electrode surface is small so that non-uniformin-plane dissolution is suppressed, and the crystal orientation propertyof crystals exposed to the top surface is small in change even when theanalysis is repeated, thereby it becomes possible to suppress surfacestate variations, and it becomes possible to stably perform liquidsubstitution of an analyte liquid and a cleaning fluid, thereby avariation in the electrochemical reaction being made small for a longtime, and enabling to obtain stable measurement results.

Embodiment 7

Embodiment 7 of the present invention will be explained. In Embodiment7, iterative analytical measurement was performed pursuant to themeasurement method of Embodiment 5 except that uric acid of a knownconcentration was used as the analyte, that the base metal was an alloyof platinum and 1% rhodium, and that the metal oxide dispersed in thebase material was zirconium oxide. The content of the metal oxidedispersed in the base material was 0.15% in the metal-equivalent value.In the measurement solution vessel 8, an analyte sample was caused to beacted on with uricase, thereby producing hydrogen peroxide. A solutionunder measurement containing hydrogen peroxide from the measurementsolution vessel 8 and a buffer fluid from the buffer fluid vessel 9 wereintroduced into the solution inlet pipe 13 to be mixed together andinjected into the electrolysis cell 1 by the solution injectionmechanism 12 so that electrochemical measurement was performed. As aresult of repeated execution of the measurement, as shown in FIG. 17, itwas found that the obtained variation range between the first and the60,000th analyses was 5.3%, which is less than that of ComparativeExample 5. This ascertained advantageous effects that in the analyzerusing the present electrode as its working electrode, etching ratedifference within the electrode surface is small so that non-uniformin-plane dissolution is suppressed, and the crystal orientation propertyof crystals exposed to the top surface is small in change even when theanalysis is repeated, thereby it becomes possible to suppress surfacestate variations, and it becomes possible to stably perform liquidsubstitution of an analyte liquid and a cleaning fluid, thereby avariation in the electrochemical reaction being made small over a longtime, and enabling to obtain stable measurement results.

Embodiment 8

Embodiment 8 of the present invention will be explained. In Embodiment8, iterative analytical measurement was performed pursuant to themeasurement method of Embodiment 5 except that creatinine of a knownconcentration was used as the analyte and that the metal oxide dispersedin the base material was zirconium oxide. The content of the metal oxidedispersed in the base material was 0.9% in the metal-equivalent value.It should be noted here that, although an electrode with the content ofthe metal oxide dispersed in the base material in excess of 1% wasproduced by way of trial, the machinability became impaired duringadjustment of the electrode shape and, in the present embodiment, theelectrode was adjusted so that it becomes 1% or less. In the measurementsolution vessel 8, an analyte sample was caused to be acted on withcreatininase and sarcosine oxidase sequentially, thereby producinghydrogen peroxide. A solution under measurement containing hydrogenperoxide from the measurement solution vessel 8 and a buffer fluid fromthe buffer fluid vessel 9 were introduced into the solution inlet pipe13 to be mixed together and injected into the electrolysis cell 1 by thesolution injection mechanism 12 so that electrochemical measurement wasperformed. As a result of repeated execution of the measurement, asshown in FIG. 17, it was revealed that the obtained variation rangebetween the first and the 60,000th analyses was 7.7%, which is less thanthat of Comparative Example 6. This ascertained advantageous effectsthat in the analyzer using the present electrode as its workingelectrode, etching rate difference within the electrode surface is smallso that non-uniform in-plane dissolution is suppressed, and the crystalorientation property of crystals exposed to the top surface is small inchange even when the analysis is repeated, thereby it becomes possibleto suppress surface state variations, and it becomes possible to stablyperform liquid substitution of an analyte liquid and a cleaning fluid,thereby a variation in the electrochemical reaction being made smallover a long time and enabling to obtain stable measurement results.

Embodiment 9

Embodiment 9 of the present invention will be explained. In Embodiment9, iterative analysis measurement was performed pursuant to themeasurement method of Embodiment 8 except that the content of the metaloxide dispersed in the base material was 0.004% in the metal-equivalentvalue. As a result of repeated execution of the measurement, as shown inFIG. 17, it was revealed that the obtained variation range between thefirst and the 60,000th analyses was 12.3%, which is slightly less thanthat of Comparative Example 7 so that a certain effect was seen butthere was no great difference. This is speculated to be due to thereasons that in the analyzer using the present electrode as its workingelectrode, the content of the metal oxide in the base material is toosmall so that miniaturization of the crystalline texture of the basematerial did not progress appreciably and the crystal orientation ratiois less than that of Embodiment 8.

Embodiment 10

Embodiment 10 of the present invention will be explained. In Embodiment10, iterative analytical measurement was done pursuant to themeasurement method of Embodiment 3 except that fatty acid of a knownconcentration was used as the analyte. More specifically, an analytesample was caused to be acted on with acyl-CoA-oxidase in themeasurement solution vessel 8, thereby producing hydrogen peroxide. Asolution under measurement containing hydrogen peroxide from themeasurement solution vessel 8 and a buffer fluid from the buffer fluidvessel 9 were introduced into the solution inlet pipe 13 to be mixedtogether and injected into the flow cell 20 by a solution suctionmechanism 15, so that electrochemical measurement was performed. As aresult of repeated execution of the measurement, as shown in FIG. 17, itwas found that the obtained variation range between the first and the60,000th analyses was 5.1%, which is less than that of ComparativeExample 8. This ascertained advantageous effects that in the analyzerusing the present electrode as its working electrode, etching ratedifference within the electrode surface is small so that non-uniformin-plane dissolution is suppressed, and the crystal orientation propertyof crystals exposed to the top surface is small in change even when theanalysis is repeated, thereby it becomes possible to suppress surfacestate variations, and it becomes possible to stably perform liquidsubstitution of an analyte liquid and a cleaning fluid, thereby avariation in the electrochemical reaction being made small over a longtime, and enabling to obtain stable measurement results.

Embodiment 11

Embodiment 11 of the present invention will be explained. In Embodiment11, iterative analytical measurement was done pursuant to themeasurement method of Embodiment 3 except that bilirubin of a knownconcentration was used as the analyte. More specifically, an analytesample was caused to be acted on with bilirubin oxidase in the presenceof potassium ferricyanide, thereby producing potassium ferrocyanide. Asolution under measurement containing potassium ferrocyanide from themeasurement solution vessel 8 and a buffer fluid from the buffer fluidvessel 9 were introduced into the solution inlet pipe 13 to be mixedtogether and injected into the flow cell 20 by the solution suctionmechanism 15, so that electrochemical measurement was performed. As aresult of repeated execution of the measurement, as shown in FIG. 17, itwas found that the obtained variation range between the first and the60,000th analyses was 5.3%, which is less than that of ComparativeExample 9. This ascertained advantageous effects that in the analyzerusing the present electrode as its working electrode, etching ratedifference within the electrode surface is small so that non-uniformin-plane dissolution is suppressed, and the crystal orientation propertyof crystals exposed to the top surface is small in change even when theanalysis is repeated, thereby it becomes possible to suppress surfacestate variations, and it becomes also possible to stably perform liquidsubstitution of an analyte liquid and a cleaning fluid, thereby avariation in the electrochemical reaction being made small over a longtime, and enabling to obtain stable measurement results.

Embodiment 12

In Embodiment 12, an electrode was fabricated with a metal base made oftitanium and its surface platinum plated and a film formed by applyingzirconium oxide and being sintered. A detailed explanation of thefabrication method will be given below. After having degreased andrinsed a titanium plate of 10 mm×10 mm and 0.5 mm in thickness, it wastreated with a 5% hydrofluoric acid aqueous solution for 2 minutes.After rinsing with water, plating was performed for 1 minute in asulfuric acid aqueous solution containing diamminedinitritoplatinum at15 mA/cm². Next, heating was done at 400° C. in the air for 1 hour.Next, after a butanol solution of chloroplatinic acid (10 g/L inplatinum metal equivalent) and an ethanol solution of zirconium chloride(1 g/L in zirconium metal equivalent) are mixed together by the equalamount to prepare a coating liquid, this coating liquid was used tomeasure 3 μL per 1 cm², and applied to a platinum-plated titanium basesubstance. Thereafter, it was vacuum-dried at room temperature for 30minutes and further sintered in the air at 500° C. for 10 minutes. Thisprocess was repeated fifty times whereby a zirconium oxide-dispersedplatinum electrode was obtained. The metal oxide content ratio of thiselectrode was 9.7%. As a result of X-ray diffraction measurement of theelectrode surface, the preferential orientation ratio was 47%. Using theelectrochemical analyzer of FIG. 1 which uses the aforementionedelectrode as its working electrode, measurement was performed in asimilar manner to Embodiment 1 by a method for immunologically analyzingas the measurement solution a TSH in blood serum and for introducing,for example, potassium hydroxide aqueous solution as a cleaning liquidinto the electrolysis cell at each measurement completion. A measurementresult revealed that the obtained variation range between the first andthe 60,000th analyses was 8.7% as shown in FIG. 17.

Embodiment 13

In Embodiment 13, iterative analytical measurement was performed in asimilar way to Embodiment 12 except that the zirconium oxide wasreplaced with a niobium oxide. As a result of the measurement, it wasfound that the obtained variation range between the first and the60,000th analyses was 9.4% as shown in FIG. 17.

Embodiment 14

In Embodiment 14, analysis measurement was repeatedly performed in asimilar way to Embodiment 12 except that the zirconium oxide wasreplaced by a tantalum oxide. As a result of the measurement, it wasfound that the obtained variation range between the first and the60,000th analyses was 9.2% as shown in FIG. 17.

In the case of using the electrodes of Embodiments 12 to 14, there wasan effect on reduction of the variation range when compared withComparative Example 1; however, such effect was smaller than that ofEmbodiment 1. It is considered that this is because the electrodes ofEmbodiments 12 to 14 are those fabricated by applying and sinteringprocesses and are larger than Embodiment 1 in concentration of the metaloxide contained in the base material and smaller in the crystalorientation ratio. Namely, it is perceived that the etching ratedifference within the electrode surface becomes greater as the surfaceetching progresses to allow a specific plane to dissolve preferentiallywhereby large step-like differences were locally generated in theelectrode surface. In addition, a phenomenon was also observed ofdropping of the electrode material with the progress of surface etchingsince it is the zirconium oxide-dispersed platinum electrode fabricatedby applying and sintering processes so that it is lower in the filmstrength compared with the rolled electrode of Embodiment 1.Furthermore, it is also conceivable that the largeness of metal oxideconcentration affected the electrochemical reaction. As a result, it canbe considered that the variation of the electrode surface state becomeslarge so that stable implementation of liquid substitution of an analyteliquid and a cleaning fluid becomes unable, thus causing the variationof electrochemical response to increase in a long-term view.

Embodiment 15

Next, Embodiment 15 of the present invention will be explained. ThisEmbodiment 15 is similar to Embodiment 1 except that the workingelectrode 2 was fabricated by integrally laminating the platinum and thevalve metal.

Here, the working electrode 2 was produced by a working electrodemanufacturing apparatus 52 shown in FIG. 18 in a procedure describedbelow.

In FIG. 18, the platinum is pressed by a platinum plate machining unit52 a at 30 MPa in a nitrogen atmosphere. Then, at the platinum machiningunit 52 a, the platinum plate is heated up to 800 degrees for 1 hour andsubjected to hot rolling at 100 MPa, thereby fabricating a platinumplate of 5 mm in thickness. Subsequently, at a platinum plate coldrolling unit 52 b, the platinum plate that was machined in the rollingunit 52 a is cold rolled at 100 MPa, thereby forming a platinum platewith a thickness of 1 mm. Thereafter, at a surface oxide film removingunit 52 c, the platinum plate that was processed in the platinum platecold rolling unit 52 b and a titanium plate of 0.5 mm in thickness areintroduced into a vacuum chamber for performing dry etching of thetitanium plate surface to thereby remove the surface oxide layer.Thereafter, by a multilayer electrode forming unit 52 d, the platinumplate and the titanium plate are rapidly laminated together and coldrolled in a vacuum at 450 degrees in such a manner that the filmthickness of the platinum plate becomes 100 μm, thereby obtaining amultilayer electrode of platinum/titanium having at its platinum part alayered crystal texture with a thickness of 5 μm or less.

Next, the multilayer electrode that was formed by the multilayerelectrode forming unit 52 d is cut at a cutting unit 52 e into a size of5 mm×15 mm. Thereafter, the cut multilayer electrode is at anelectroding unit 52 f bent with its end portion by 90 degrees and theplatinum surface and a conductive wire are connected together bysoldering.

Next, at a resin embedding unit 52 g, it is buried in a fluorine-basedresin using an adhesive agent in such a manner that only the platinumsurface of the multilayer electrode is exposed by its area of 5 mm×10mm.

Subsequently, at a mechanical polishing unit 52 h, the platinum surfaceis mechanically polished using water-proof abrasive paper, diamondpaste, and alumina particles sequentially, thus obtaining a mirrorfinished plane.

Finally, at an electrolytic polishing unit 52 i, electrical potentialscanning between potential levels of −1.2 to 1.0V vs. Ag|AgCl isrepeated 10,000 times at a potential scanning rate of 0.1 V/s in a 0.2mol/L potassium hydroxide aqueous solution, thereby obtaining theworking electrode 2.

X-ray diffraction measurement was performed of the electrode surface ofthe working electrode 2 used in this Embodiment 15. CuKα was used as anX-ray source to measure three different points on the platinum surfacewith output settings of 40 kV and 20 mA. Integration values (I) ofdiffraction peaks of a (111) plane, a (200) plane, a (220) plane, and a(311) plane on the platinum surface were calculated to thereby obtaineach direction's orientation ratio ((%)=I(hkl)/ΣI(hkl)×100).Incidentally, the calculation of each peak integration value was done inranges of 37°≦2θ≦42° for the (111) plane, 44°≦2θ≦49° for the (200)plane, 65°≦2θ≦70° for the (220) plane, 78°≦2θ≦83° for the (311) plane,respectively (where θ is the diffraction angle). As results of themeasurement, it was revealed that the plane index (220) ifpreferentially oriented with its orientation ratio of 97% as in theresult of Embodiment 15 shown in FIG. 19.

The through-thickness cross-section of a similarly produced multilayerelectrode was exposed and its platinum part was analyzed by means of anelectron beam backscatter pattern. Analysis results are shown in FIG.20A and FIG. 20B.

As shown in FIG. 20A, it was found that the obtained working electrodehas a layered crystal texture with respect to the electrode surface. Tocalculate the thickness of a platinum crystal layer, an area of 25 μm×25μm was subjected to measurement of three fields of view while letting aregion of 0.075 μm×0.075 μm be data of one point and the thickness of alayer having a maximal layer thickness in the measured surface wasmeasured.

A typical near-surface crystal texture image of the present electrode isshown in FIG. 20B. The layer thickness was found to be 5 μm or less atmost.

FIG. 21 is a diagram for explanation of an effect of the platinumelectrode employed in Embodiment 15 of the present invention. Note thatthe data shown in FIG. 21 is the date obtained by repeated execution ofmeasurement with TSH (thyroid-stimulating hormone) of the sameconcentration as the analyte. The abscissa of FIG. 21 indicates thenumber of times of testing and the ordinate indicates a value of eachmeasurement value divided by a reference value. Furthermore, thereference value is an output value upon measurement of a TSH-containingsolution of a pre-determined concentration and the actual measurementvalue is a measured value obtained when measuring each of the solutionsused in Embodiment 15 and Comparative Example 10. The variation range isdefined to be a difference between values of the 60,000th and the firstanalyses.

In FIG. 21, lines connecting circles are in the case of Embodiment 15 ofthe present invention; lines connecting triangles are in the case ofComparative Example 10 different from the present invention.

By using the electrochemical analyzer of FIG. 1, measurement wasperformed by a method for immunologically analyzing as the measurementsolution a chemical component contained in a liquid sample such as bloodor urine—for example, TSH in blood serum—and introducing, for example,potassium hydroxide aqueous solution as a cleaning fluid into theelectrolysis cell at every completion of each measurement.

As shown in FIG. 21, the variation range in the case of using anelectrode of the comparative example was 10.3%. The electrode ofComparative Example 10 is a multilayer electrode of platinum andtitanium subjected to hot rolling and recrystallization treatments andis the electrode that underwent mechanical polishing and electrolytictreatment of the platinum surface in a similar way to Embodiment 15.Details will be explained in Comparative Examples described later. Incontrast, in the case of using the platinum electrode of Embodiment 15of the present invention, the variation range was reduced to 4.4%.

The electrode of Embodiment 15 of the present invention is themultilayer electrode in which the platinum part's cross-section crystaltexture in the plate thickness direction is formed in the form of layerswith respect to the electrode surface with a layer thickness being lessthan or equal to 5 μm. And, in the electrode in accordance withEmbodiment 15 of this invention the surface alteration layer with adisordered crystal orientation property created in rolling andmechanical polishing processes was removed away and it is preferentiallyoriented in the plane direction (220) with its orientation ratio of 90%or higher. It was revealed that in the electrochemical analyzer usingthe electrode of Embodiment 15 of the present invention as its workingelectrode, since the etching rate difference within the electrodesurface is small, the unevenness created due to etching is small and itbecomes possible to suppress variations of the surface area so that thevariation in the electrochemical response is small over a long time,thereby making it possible to obtain stable measurement results.

Embodiment 16

Next, Embodiment 16 of the present invention will be explained. Anelectrode of this Embodiment 16 and an electrochemical analyzer using itare similar to those of Embodiment 15 except that in the manufacture ofthe electrode the aforementioned electrode was immersed in a prescribedelectrolytic solution during electrolytic polishing processing so thatan alteration layer of the platinum surface was removed while diagnosingby cyclic voltammetry the surface state.

The cyclic voltammetry was conducted under conditions of using anitrogen-substituted phosphoric acid buffer solution of a pH of 6.86 asthe electrolytic solution, a platinum wire as the working electrode,Ag|AgCl as the reference electrode, the potential scanning range of −0.6to 1.1 V, and the scanning rate of 0.1 V/s. A measurement result isshown in FIG. 22. For comparison purposes, a result of ComparativeExample 10 is shown together.

Among a plurality of hydrogen absorption/desorption current peaksobtained from the result of cyclic voltammetry, letting “a” be a peakobserved in a range of −0.37 to −0.31 V and “b” be a peak seen in arange of −0.31 to −0.2 V, their peak areas and an area ratio b/a arecalculated. Electrolytic treatment was performed until the area ratiobecomes 80% or less; thus, the working electrode 2 was obtained.

As a result of iterative analysis by the electrochemical analyzer usingthe working electrode in accordance with Embodiment 16 of the presentinvention in a similar way to Embodiment 15, an excellent result of thevariation range of 4.2% was obtained. As a result of X-ray diffractionanalysis of an electrode which was fabricated in a similar way and isdifferent from the present invention, it was observed to be preferentialoriented in the (220) direction with an orientation ratio of 98%. In theelectron beam backscatter pattern analysis also, the thickness of acrystal texture layer of platinum plate-thickness cross-section was 5 μmor less. In an analyzer using as its working electrode the electrode inaccordance with Embodiment 16 of this invention, since the etching ratedifference within the electrode surface is small, the unevenness createddue to etching is small and it becomes possible to suppress variationsof the surface area so that the variation in the electrochemicalresponse is small over a long time, thereby making it possible to obtainstable measurement results.

Although in Embodiment 16 of this invention the peaks a and b are usedas the criterion for judgment of degree of the surface alteration layerremoval, it was ascertained that similar results are also obtainable bycalculating a ratio b/c from the peak c seen in the range of −0.48 to−0.37 V and the peak b and for letting b/c be 35% or less as thecriterion.

Embodiment 17

An electrochemical analysis apparatus in accordance with Embodiment 17of the present invention is similar to the electrochemical analyzer ofEmbodiment 2 except for the manufacturing method of the workingelectrode 34.

Here, in FIG. 11, a flow cell 20 serving as an electrolysis cell isformed by laminating two electrically insulative substrates 30 and 32and a sealing member 31 shown in FIG. 11A in a way shown in FIG. 11B.The insulative substrate 30 is made of polyether ether ketone. Thematerial of this insulative substrate 30 is not specifically limitedthereto as far as it is an insulative resin excellent in chemicalresistance; fluorine-based resin, polystyrene, polyethylene,polypropylene, polyester, polyvinyl chloride, epoxy resin, polyimide,polyamide-imide, polysulfone, polyether sulfone, polyphenylene sulfide,acrylic resin, and the like may be used.

On one surface of the insulative substrate 30 (the surface opposing theelectrically insulative substrate 32), a working electrode 34 is fixed.A manufacturing method of the working electrode 34 will be shown below.

Namely, those processes prior to the mechanical polishing of Embodiment15 of the present invention were performed to obtain a platinum/titaniummultilayer electrode. This multilayer electrode was embedded in adepression portion provided in the surface of the insulative substrate30 and, after bonded by an adhesive agent, mechanical polishing wasapplied thereto using water-proof abrasive paper, diamond paste, andalumina particles sequentially until a step-like surface differencebetween the insulative substrate 30 and the multilayer electrodedisappeared, thereby obtaining a mirror-finished surface. Incidentally,as for the adhesive agent a resin material with thermoplasticity,thermalsetting, or photohardening such as an epoxy-based or acrylicsubstance may be used; it is not specifically limited thereto and may beproperly chosen as long as it is excellent in chemical resistancesimilar to the insulative resin. [0063] Thereafter, application ofelectrical potential having rectangular pulses of −1.2 V/0.5 sec and 3.0V/1.5 sec was repeated 10,000 times in 0.2 mol/L potassium hydroxideaqueous solution.

In Embodiment 17 of the present invention, the working electrode 4 wasplaced so that the rolling direction is perpendicular to the directionalong which a liquid flows during analysis.

As a result of X-ray diffraction measurement of the electrode surface ofthe working electrode 34 used in this Embodiment 17 it was revealed thatthe plane index (220) was preferentially oriented with its orientationratio is 92%. It was also revealed by electron beam backscatter patternanalysis that the working electrode 34 has a laminar crystal texturewith respect to the electrode surface and that the layer thickness ofplatinum is 5 μm or less at most.

By using the electrochemical analyzer shown in FIG. 10, measurement wasdone by a method for analyzing as the measurement solution a chemicalcomponent contained in a liquid sample such as blood or urine—forexample, a compound with TSH in blood serum being adsorbed in thesurface of a magnetic bead(s) with a diameter of 3 μm—and introducing asa cleaning fluid, for example, potassium hydroxide aqueous solution intothe electrolysis cell at every completion of each measurement.

The variation range between the first and the 60,000th analyses wasobtained in a similar way to Embodiment 15 to be 5.1%. In the analyzerusing the electrode of Embodiment 17 of the present invention as itsworking electrode, since the etching rate difference within theelectrode surface is small, the unevenness created due to etching issmall and it becomes possible to suppress variations of the surfacearea. It was ascertained that it becomes also possible to stably performliquid substitution of an analyte liquid and a cleaning fluid so thatthe variation in the electrochemical response is small for a long timeperiod, thereby enabling stable measurement results to be obtained.

In addition, another effect was recognized that the beads are preventedfrom flowing downstream from the working electrode by disposing theworking electrode such that its rolling direction is perpendicular tothe flow direction of the analyte liquid, thereby making it possible toobtain stable measurement results with small variations over a longtime.

Incidentally, in this Embodiment 17 the working electrode 34 is placedso that its rolling direction is perpendicular to the direction of theanalyte liquid flowing; however, the case of setting the rollingdirection to the same direction as the flow direction was investigatedant the results revealed that the variation range was 7%, which isslightly greater than that of the present Embodiment 17. The datastability within a short period of time was also evaluated to revealthat data variability becomes larger when compared to this embodiment.This is considered to be due to the influence of slight downstreamoutflow of the magnetic beads from the working electrode surface duringanalysis.

Thus, it was found that, as shown in this Embodiment 17, it is a morepreferable form for improvement of the data stability to place theworking electrode 34 so that the rolling direction is perpendicular tothe analyte liquid's flow direction during analysis.

Embodiment 18

Next, Embodiment 18 of the present invention will be explained. InEmbodiment 18, enzyme is immobilized on the surface of the electrode ofEmbodiment 15, with an underlayer metal being made of Nb. The otherarrangements are similar to those of Embodiment 15. In Embodiment 18,iterative measurement was performed in a similar way to Embodiment 15while letting glucose of a known concentration be the analyte.

As a result of measurement, as shown in FIG. 24, it was found that thevariation range between the first and the 60,000th analyses was 4.1%,which is less than that of Comparative Example 11 with glucose as itsanalyte. This is because, in the analyzer using the electrode ofEmbodiment 18 of the present invention as its working electrode, sincethe etching rate difference within the electrode surface is small, theunevenness created due to etching is small, and it becomes possible tosuppress variations of the surface area, resulting in achievement of anability to stably control the amount of enzyme modifying on theelectrode surface. In addition, it is ascertained that according toEmbodiment 18 of this invention it becomes possible to stably performliquid substitution of an analyte liquid and a cleaning fluid so thatthe variation in the electrochemical response is small over a long time,thereby making it possible to obtain stable measurement results.

As for Comparative Example 11 shown in FIG. 24, its explanation will begiven later.

Embodiment 19

Next, Embodiment 19 of the present invention will be explained. InEmbodiment 19, iterative analytical measurement was performed pursuantto the measurement method of Embodiment 15 except that urea of a knownconcentration was taken as the analyte. Namely, in the measurementsolution vessel 8, an analyte sample was caused to be acted on withurease, next with β-nicotinamide adenine dinucleotide (NADH), andfurther with glutamate dehydrogenase in the presence of potassiumferricyanide, thereby producing a potassium ferrocyanide.

A solution under measurement containing potassium ferrocyanide from themeasurement solution vessel 8 and a buffer fluid from the buffer fluidvessel 9 were introduced into the solution inlet pipe 13 to be mixedtogether and then injected into the electrolysis cell 1 by the solutioninjection mechanism 12 so that electrochemical measurement was done. Asa result of repeated execution of such measurement, as shown in FIG. 24,it was found that the obtained variation range between the first and the60,000th analyses was 2.8%, which is less than that of ComparativeExample 12 using the same analyte.

This is because in the analyzer using this electrode as its workingelectrode, since the etching rate difference within the electrodesurface is small, the unevenness created due to etching is small and itis possible to suppress variations of the surface area.

Additionally, it is ascertained that according to Embodiment 19 of thepresent invention it becomes possible to stably perform liquidsubstitution of an analyte liquid and a cleaning fluid so that thevariation in the electrochemical response is small over a long time,thus making it possible to obtain stable measurement results.

Embodiment 20

Next, Embodiment 20 of the present invention will be explained.Embodiment 20 is such that the underlayer metal is Zr. The otherarrangements are similar to those of Embodiment 15. In Embodiment 20,cholesterol of a known concentration was taken as the analyte, anditerative analytic measurement was performed pursuant to the measurementmethod of Embodiment 15.

Namely, in the measurement solution vessel 8 of FIG. 1, an analytesample was caused to be acted on with cholesterol oxidase to producehydrogen peroxide. Then, a measurement solution containing hydrogenperoxide from the measurement solution vessel 8 and a buffer fluid fromthe buffer fluid vessel 9 were introduced into the solution inlet pipe13 to be mixed together and then injected into the electrolysis cell 1by the solution injection mechanism 12 so that electrochemicalmeasurement was performed.

As a result of repeated execution of the measurement, as shown in FIG.24, the obtained variation range between the first and the 60,000thanalyses was found to be 5.8%, which is less than that of ComparativeExample 13 using the same analyte. This is because in the analyzer usingthis electrode as its working electrode, since the etching ratedifference within the electrode surface is small, the unevenness createddue to etching is small and it becomes possible to suppress variationsof the surface area.

Additionally, it is ascertained that according to Embodiment 20 of thepresent invention it becomes possible to stably perform liquidsubstitution of an analyte liquid and a cleaning fluid so that thevariation in the electrochemical response is small over a long time,thus making it possible to obtain stable measurement results.

Embodiment 21

Next, Embodiment 21 of the present invention will be explained. InEmbodiment 21, analytical measurement was repeatedly performed pursuantto the measurement method of Embodiment 15 except that in Embodiment 21taken as its analyte uric acid of a known concentration.

Namely, in the measurement solution vessel 8, an analyte sample wascaused to be acted on with uricase to produce hydrogen peroxide. Ameasurement solution containing hydrogen peroxide from the measurementsolution vessel 8 and a buffer fluid from the buffer fluid vessel 9 wereintroduced into the solution inlet pipe 13 to be mixed together and theninjected into the electrolysis cell 1 by the solution injectionmechanism 12 so that electrochemical measurement was done.

As a result of repeated execution of the measurement, as shown in FIG.24, the obtained variation range between the first and the 60,000thanalyses was found to be 6.5%, which is less than that of ComparativeExample 14 using the same analyte. This is because in the analyzer usingthis electrode as its working electrode, since the etching ratedifference within the electrode surface is small, the unevenness createddue to etching is small and it becomes possible to suppress variationsof the surface area.

Additionally, it is ascertained that according to Embodiment 21 of thepresent invention it becomes possible to stably perform liquidsubstitution of an analyte liquid and a cleaning fluid so that thevariation in the electrochemical response is small over a long time,thereby making it possible to obtain stable measurement results.

Embodiment 22

Next, Embodiment 22 of the present invention will be explained. InEmbodiment 22, analytical measurement was repeatedly performed pursuantto the measurement method of Embodiment 15 except that in Embodiment 22creatinine of a known concentration is taken as its analyte.

Namely, in the measurement solution vessel 8, an analyte sample wascaused to be acted on with creatininase and sarcosine oxidasesequentially to produce hydrogen peroxide. A measurement solutioncontaining hydrogen peroxide from the measurement solution vessel 8 anda buffer fluid from the buffer fluid vessel 9 were introduced into thesolution inlet pipe 13 to be mixed together and then injected into theelectrolysis cell 1 by the solution injection mechanism 12 so thatelectrochemical measurement was performed.

As a result of repeated execution of the measurement, as shown in FIG.24, the obtained variation range between the first and the 60,000thanalyses was found to be 7.9%, which is less than that of ComparativeExample 15 using the same analyte. This is because in the analyzer usingthis electrode as its working electrode, since the etching ratedifference within the electrode surface is small, the unevenness createddue to etching is small and it becomes possible to suppress variationsof the surface area.

Additionally, it is ascertained that according to Embodiment 22 of thepresent invention it becomes possible to stably perform liquidsubstitution of an analyte liquid and a cleaning fluid so that thevariation in the electrochemical response is small in variation over along time, thus making it possible to obtain stable measurement results.

Embodiment 23

Next, Embodiment 23 of the present invention will be explained. InEmbodiment 23, analytical measurement was repeatedly performed pursuantto the measurement method of Embodiment 15 except that in Embodiment 23creatinine of a known concentration is taken as its analyte.

An analyte sample was caused to be acted on with creatininase andsarcosine oxidase sequentially to produce hydrogen peroxide. A solutionunder measurement containing hydrogen peroxide from the measurementsolution vessel 8 and a buffer fluid from the buffer fluid vessel 9 wereintroduced into the solution inlet pipe 13 to be mixed together and theninjected into the electrolysis cell 1 by the solution injectionmechanism 12 so that electrochemical measurement was performed.

As a result of repeated execution of the measurement, as shown in FIG.24, the obtained variation range between the first and the 60,000thanalyses was found to be 9.8%, which is less than that of ComparativeExample 16 using the same analyte. This is because in the analyzer usingthis electrode as its working electrode, since the etching ratedifference within the electrode surface is small, the unevenness createddue to etching is small and it becomes possible to suppress variationsof the surface area.

Additionally, it is ascertained that according to Embodiment 23 of thepresent invention it becomes possible to stably perform liquidsubstitution of an analyte liquid and a cleaning fluid so that thevariation in the electrochemical response is small over a long time,thus making it possible to obtain stable measurement results.

Embodiment 24

Next, Embodiment 24 of the present invention will be explained. InEmbodiment 24, analytical measurement was repeatedly performed pursuantto the measurement method of Embodiment 15 except that in Embodiment 24fatty acid of a known concentration is taken as the analyte.

Namely, in the measurement solution vessel 8, an analyte sample wascaused to be acted on with acyl-CoA-oxidase to produce hydrogenperoxide. A solution under measurement containing hydrogen peroxide fromthe measurement solution vessel 8 and a buffer fluid from the bufferfluid vessel 9 were introduced into the solution inlet pipe 13 to bemixed together and then injected into the electrolysis cell 1 by thesolution injection mechanism 12 so that electrochemical measurement wasperformed.

As a result of repeated execution of the measurement, as shown in FIG.24, the obtained variation range between the first and the 60,000thanalyses was found to be 5.9%, which is less than that of ComparativeExample 17 using the same analyte.

This is because in the analyzer using this electrode as its workingelectrode, since the etching rate difference within the electrodesurface is small, the unevenness created due to etching is small and itbecomes possible to suppress variations of the surface area.

Additionally, it is ascertained that according to Embodiment 24 of thepresent invention it becomes possible to stably perform liquidsubstitution of an analyte liquid and a cleaning fluid so that thevariation in the electrochemical response is small over a long time,thus making it possible to obtain stable measurement results.

Embodiment 25

Next, Embodiment 25 of the present invention will be explained. InEmbodiment 25, analytical measurement was repeatedly performed pursuantto the measurement method of Embodiment 15 except that in Embodiment 25used bilirubin of a known concentration is taken as the analyte.

Namely, in the measurement solution vessel 8, an analyte sample wascaused to be acted on with bilirubin oxidase in the presence ofpotassium ferricyanide to produce potassium ferrocyanide. A solutionunder measurement containing potassium ferrocyanide from the measurementsolution vessel 8 and a buffer fluid from the buffer fluid vessel 9 wereintroduced into the solution inlet pipe 13 to be mixed together and theninjected into the electrolysis cell 1 by the solution injectionmechanism 12 so that electrochemical measurement was done.

As a result of repeated execution of the measurement, as shown in FIG.24, the obtained variation range between the first and the 60,000thanalyses was found to be 4.3%, which is less than that of ComparativeExample 18 using the same analyte.

This is because in the analyzer using this electrode as its workingelectrode, since the etching rate difference within the electrodesurface is small, the unevenness created due to etching is small and itbecomes possible to suppress variations of the surface area.

Additionally, it is ascertained that according to Embodiment 25 of thepresent invention it becomes possible to stably perform liquidsubstitution of an analyte liquid and a cleaning fluid so that thevariation in the electrochemical response is small over a long time,thus making it possible to obtain stable measurement results.

Comparative Example 1

A working electrode 2 of the comparative example is an electrode withplatinum being rolled to a plate-like shape. It was heated up to 800° C.for 1 hour and hot rolled at 100 MPa so that its thickness becomes 0.1mm. After cooling, it was embedded in fluorine-based resin, subjected tomechanical polishing by sequentially using water-proof abrasive paper,diamond paste, and alumina, and continuously subjected to electrolyticpolishing, thereby obtaining the working electrode in a similar way toEmbodiment 1.

Using this working electrode in the electrochemical analyzer of FIG. 1,measurement was performed, similar to Embodiment 1, by a method forimmunologically analyzing as the measurement solution TSH in blood serumand introducing as a cleaning fluid, for example, potassium hydroxideaqueous solution into the electrolysis cell at every completion of eachmeasurement.

As a result, as shown in FIG. 6, a variation range in the case of usingthe electrode of the comparative example was 10.3%. As the electrode ofthe comparative example was analyzed by X-ray diffraction, it wasrevealed to be preferentially oriented to (220) and (111) as shown inFIG. 5; however, the orientation ratio of the (220) direction exhibitinga maximal intensity was found to be 54%. In addition, observation of thecrystalline texture of the cross-section in the plate thicknessdirection of the electrode of Comparative Example 1 revealed that itcontains coarse crystal textures with large grain sizes. It isconsidered to be attributed to production of large step-like differenceslocally in the electrode plane by the etching rate difference within theelectrode surface being large and a specific plane dissolvingpreferentially with repeated execution of analysis, that is, with theprogress of surface etching in the case of using such an electrode.Also, the orientation ratios of respective crystalline directionsexposed to the top surface change with repeated execution of analysis.As a result, it is considered that the variation of the electrodesurface state becomes large and it becomes impossible to stably performliquid substitution of an analyte liquid and a cleaning fluid, therebycausing the variation of the electrochemical response to become largewhen looking at on a long-term basis.

Comparative Example 2

Comparative Example 2 used as its working electrode the platinumelectrode shown in FIG. 17 which was fabricated in a similar way toComparative Example 1, and performed iterative measurement with glucosebeing its analyte similar to Embodiment 4. A result of the measurementrevealed that the obtained variation range between the first and the60,000th analyses was 4.2% as shown in FIG. 17.

Comparative Example 3

Comparative Example 3 used as its working electrode the platinumelectrode shown in FIG. 17 which was formed in a similar way toComparative Example 1, and performed iterative measurement with ureabeing its analyte similar to Embodiment 5. A result of the measurementrevealed that the obtained variation range between the first and the60,000th analyses was 3.7% as shown in FIG. 17.

Comparative Example 4

Comparative Example 4 used as its working electrode the platinumelectrode shown in FIG. 17 which was formed in a similar way toComparative Example 1, and performed iterative measurement withcholesterol being its analyte similar to Embodiment 6. A result of themeasurement revealed that the obtained variation range between the firstand the 60,000th analyses was 7.3% as shown in FIG. 17.

Comparative Example 5

Comparative Example 5 used as its working electrode the platinumelectrode shown in FIG. 17 which was formed in a similar way toComparative Example 1, and performed iterative measurement with uricacid being its analyte similar to Embodiment 7. A result of themeasurement revealed that the obtained variation range between the firstand the 60,000th analyses was 8.8% as shown in FIG. 17.

Comparative Example 6

Comparative Example 6 used as its working electrode the platinumelectrode shown in FIG. 17 which was formed in a similar way toComparative Example 1, and performed iterative measurement withcreatinine being its analyte similar to Embodiment 8. A result of themeasurement revealed that the obtained variation range between the firstand the 60,000th analyses was 11.2% as shown in FIG. 17.

Comparative Example 7

Comparative Example 7 used as its working electrode the platinumelectrode shown in FIG. 17 which was formed in a similar way toComparative Example 1, and performed iterative measurement withcreatinine being its analyte similar to Embodiment 9. A result of themeasurement revealed that the obtained variation range between the firstand the 60,000th analyses was 12.6% as shown in FIG. 17.

Comparative Example 8

Comparative Example 8 used as its working electrode the platinumelectrode shown in FIG. 17 which was formed in a similar way toComparative Example 1, and performed iterative measurement with fattyacid being its analyte similar to Embodiment 10. A result of themeasurement revealed that the obtained variation range between the firstand the 60,000th analysis was 7.2% as shown in FIG. 17.

Comparative Example 9

Comparative Example 9 used as its working electrode the platinumelectrode shown in FIG. 17 which was formed in a similar way toComparative Example 1, and performed iterative measurement withbilirubin being its analyte similar to Embodiment 11. A result of themeasurement revealed that the obtained variation range between the firstand the 60,000th analyses was 6.6% as shown in FIG. 17.

In the case of using the platinum electrodes of Comparative Examples 2to 9, it is considered to be attributed to production of large step-likedifferences locally in the electrode plane by the etching ratedifference within the electrode surface being large and a specific planedissolving preferentially with repeated execution of analysis, that is,with the progress of surface etching. As a result, it is considered thatthe variation of the electrode surface state becomes large and itbecomes impossible to stably perform liquid substitution of an analyteliquid and a cleaning fluid, thus causing the variation of theelectrochemical response to become large when viewing on a long-termbasis.

Next, Comparative Examples 10 to 18 shown in FIG. 24 will be explained.

Comparative Example 10

The electrode of Comparative Example 10 is a multilayer electrode ofplatinum and titanium. This electrode was pressed as of a platinum platewith a thickness of 1 mm and a titanium plate with a thickness of 0.5 mmat 30 MPa in vacuum. It was heated up to 800 degrees for 1 hour and hotrolled at 100 MPa so that the thickness of platinum part becomes 100 μm.After cooling, it was embedded into a fluorine-based resin similar toEmbodiment 15 of the present invention, the platinum surface wassubjected to mechanical polishing using water-proof abrasive paper,diamond paste, and alumina sequentially and continuously subjected toelectrolytic polishing, thereby obtaining the working electrode.

Using this working electrode in the electrochemical analyzer of FIG. 1similar to Embodiment 15, measurement was performed by a method forimmunologically analyzing as the measurement solution TSH in blood serumand introducing as a cleaning fluid, for example, potassium hydroxideaqueous solution into the electrolysis cell at every completion of eachmeasurement.

As a result, as shown in FIG. 21, a variation range in the case of usingthe electrode of Comparative Example 10 was about 10.3%. As theelectrode of Comparative Example 10 was analyzed by X-ray diffraction,it was revealed to be preferentially oriented to (220) and (111) asshown in FIG. 19. The orientation ratio of the (220) directionexhibiting a maximal intensity was, however, found to be 54%.

Additionally, upon observation of the crystal texture of a cross-sectionin the plate thickness direction of the platinum part by electron beambackscatter pattern analysis, it was found that the platinum has nolayered form and grain sizes were extremely coarse as shown in FIG. 23.

In the case of using such the electrode, it is considered that theetching rate difference within the electrode surface becomes large withrepeated execution of analysis, that is, with a progress of surfaceetching, causing the unevenness caused due to etching and the variationin the surface area to increase, resulting in the variation in theelectrochemical response becoming large.

Comparative Example 11

Comparative Example 11 used as its working electrode the multilayerelectrode of Comparative Example 10 with the crystal texture of theplatinum part coarsened, and performed iterative measurement withglucose being the analyte similar to Embodiment 18. A result of themeasurement revealed that as shown in FIG. 24, the obtained variationrange between the first and the 60,000th analyses was 4.2%, which isgreater than that of Embodiment 18.

Comparative Example 12

Comparative Example 12 used as its working electrode the multilayerelectrode of Comparative Example 10 with the crystal texture of theplatinum part coarsened, and performed iterative measurement with ureabeing the analyte similar to Embodiment 19. A result of the measurementrevealed that as shown in FIG. 24, the obtained variation range betweenthe first and the 60,000th analyses was 3.7%, which is greater than thatof Embodiment 19.

Comparative Example 13

Comparative Example 13 used as its working electrode the multilayerelectrode of Comparative Example 10 with the crystal texture of theplatinum part coarsened, and performed iterative measurement withcholesterol being the analyte similar to Embodiment 20. A result of themeasurement revealed that as shown in FIG. 24, the obtained variationrange between the first and the 60,000th analyses was 7.3%, which isgreater than that of Embodiment 20.

Comparative Example 14

Comparative Example 14 used as its working electrode the multilayerelectrode of Comparative Example 10 with the crystal texture of theplatinum part coarsened, and performed iterative measurement with uricacid being the analyte similar to Embodiment 21. A result of themeasurement revealed that as shown in FIG. 24, the obtained variationrange between the first and the 60,000th analyses was 8.8%, which isgreater than that of Embodiment 21.

Comparative Example 15

Comparative Example 15 used as its working electrode the multilayerelectrode of Comparative Example 10 with the crystal texture of theplatinum part coarsened, and performed iterative measurement withcreatinine being the analyte similar to Embodiment 22. A result of themeasurement revealed that as shown in FIG. 24, the obtained variationrange between the first and the 60,000th analyses was 11.2%, which isgreater than that of Embodiment 22.

Comparative Example 16

Comparative Example 16 used as its working electrode the multilayerelectrode of Comparative Example 10 with the crystal texture of theplatinum part coarsened, and performed iterative measurement withcreatinine being the analyte similar to Embodiment 23. A result of themeasurement revealed that as shown in FIG. 24, the obtained variationrange between the first and the 60,000th analyses was 12.6%, which isgreater than that of Embodiment 23.

Comparative Example 17

Comparative Example 17 used as its working electrode the multilayerelectrode of Comparative Example 10 with the crystal texture of theplatinum part coarsened, and performed iterative measurement with fattyacid being the analyte similar to Embodiment 24. A result of themeasurement revealed that as shown in FIG. 24, the obtained variationrange between the first and the 60,000th analyses was 7.2%, which isgreater than that of Embodiment 24.

Comparative Example 18

Comparative Example 18 used as its working electrode the multilayerelectrode of Comparative Example 10 with the crystal texture of theplatinum part coarsened, and performed iterative measurement withbilirubin being the analyte similar to Embodiment 25. A result of themeasurement revealed that as shown in FIG. 24, the obtained variationrange between the first and the 60,000th analyses was 6.6%, which isgreater than that of Embodiment 25.

It is considered that in the case of using such the multilayerelectrodes of Comparative Examples 11 to 18, the etching rate differencewithin the electrode surface becomes large with repeated execution ofanalysis, that is, with a progress of surface etching, causing theunevenness caused due to etching and the variation in the surface areato increase, resulting in the variation in the electrochemical responsebecoming large.

It should be noted that, although the above-stated embodiments of thepresent invention are examples where the present invention was appliedto the working electrode of an electrochemical analysis apparatus, thisinvention may be applicable not only to the working electrode but alsoto the counter electrode. Also applying the present invention to thecounter electrode makes it possible to further achieve a high accuracyof analysis data.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

REFERENCE SIGNS LIST

-   -   1 Electrolysis Cell    -   2, 34, 74, 104, 134, 194 Working Electrode    -   3, 35, 75, 105, 135, 195 Counter Electrode    -   4 Reference Electrode    -   5 Potential-Applying Means    -   6 Measuring Means    -   7, 39, 40, 79, 80, 109, 110, 139, 140, 199, 200, 302 Lead Wire    -   8 Measurement Solution Vessel    -   9 Buffer Fluid Vessel    -   10 Cleaning Liquid Vessel    -   11 Solution-Dispensing Mechanism    -   12 Solution Injection Mechanism    -   13 Solution Inlet Pipe    -   14 Solution Outlet Pipe    -   15 Solution Exhaust (Suction) Mechanism    -   16 Waste Container    -   20, 60, 90, 120, 180 Flow Cell    -   21, 22 Hole    -   30, 32, 70, 72, 100, 102, 130, 132, 190 Insulative Substrate    -   192 Insulative Chassis    -   31, 71, 101, 131 Sealing Member    -   33, 73, 103, 133, 193 Screw Hole    -   36, 76, 106, 136 Opening    -   37, 38, 77, 78, 107, 108, 137, 138, 197, 198 Pipe    -   50 Working Electrode Manufacturing Apparatus    -   50 a Electroding Unit    -   50 b Resin Embedding Unit    -   50 c Mechanical Polishing Unit    -   50 d Electrolytic Polishing Unit    -   52 Working Electrode Manufacturing Apparatus    -   52 a Platinum Plate Machining Unit    -   52 b Platinum Plate Cold Rolling Unit    -   52 c Surface Oxide Film Removing Unit    -   52 d Multilayer Electrode Forming Unit    -   52 e Cutting Unit    -   52 f Electroding Unit    -   52 g Resin Embedding Unit    -   52 h Mechanical Polishing Unit    -   52 i Potential Scanning Unit    -   141 Electrically Connecting Bolt    -   142 Electrically Connecting Plate    -   143 Thread    -   191 O-Ring    -   300 Insulative Resin    -   301 Composite Material    -   303 Adhesive Agent    -   304 Shaft

The invention claimed is:
 1. An electrode for electrochemical measurement to be used in an electrochemical analysis apparatus which measures electrochemical response of a chemical component contained in a liquid sample, the electrode made by connecting a lead wire to a composite material consisting of a base material and an oxide of a metal, the oxide of a metal selected from a group consisting of zirconium, tantalum, and niobium, and is dispersed in the base material, the base material being made of platinum or a platinum alloy, wherein a content ratio of the oxide of a metal is 0.005 to 1 weight percent (wt %).
 2. The electrode for electrochemical measurement according to claim 1, wherein an orientation ratio of one of a plurality of crystal directions obtained is 80% or greater when letting the orientation ratio (%) of a crystal direction obtained by X-ray diffraction measurement of a surface of the electrode be I(hkl)/ΣI(hkl)×100 (where I(hkl) is a diffraction intensity integration value of each plane, and ΣI(hkl) is a total sum of diffraction intensity integration values of (hkl)).
 3. The electrode for electrochemical measurement according to claim 1, wherein a material of an electrode is embedded in an insulative resin except for a part of a surface of the electrode.
 4. An electrolysis cell for measuring electrochemical response of a chemical component contained in a liquid sample, the electrolysis cell having a working electrode, a counter electrode, and a reference electrode disposed therein, the working electrode being the electrode according to claim
 1. 5. The electrolysis cell according to claim 4, wherein the electrolysis cell is a flow cell to which an injection port for injecting into the cell and an exhaust port for exhausting to outside a liquid sample are disposed.
 6. An electrochemical analysis apparatus comprising: an electrolysis cell having a working electrode, a counter electrode, and a reference electrode disposed therein; a solution injection device which injects into the electrolysis cell a solution under measurement, a buffer solution, and a cleaning solution; a potential application device which applies potentials to the working electrode, the counter electrode, and the reference electrode; and a measuring device which is connected to the working electrode, the counter electrode, and the reference electrode and measures electrochemical characteristics of the solution under measurement, the working electrode being an electrode according to claim
 1. 